[{"id":30883,"web_url":"https://patchwork.libcamera.org/comment/30883/","msgid":"","date":"2024-08-21T16:55:45","subject":"Re: [PATCH 3/5] pipeline_handler: Add acquireDevice() method to\n\tmirror existing releaseDevice()","submitter":{"id":117,"url":"https://patchwork.libcamera.org/api/people/117/","name":"Cheng-Hao Yang","email":"chenghaoyang@chromium.org"},"content":"Hi Hans,\n\nThanks for the patch. Actually in mtkisp7, we did something very similar\n[1].\n(And I just caught a bug by checking your changes. Thanks :)\n\n[1]:\nhttps://chromium-review.googlesource.com/c/chromiumos/third_party/libcamera/+/5525900\n\nOn Tue, Aug 20, 2024 at 9:50 PM Hans de Goede wrote:\n\n> ATM libcamera always keeps all /dev/video# and /dev/v4l2_subdev# nodes\n> for a pipeline open after enumerating the camera.\n>\n> This is a problem for uvcvideo and atomisp /dev/video# nodes as well as\n> for VCM /dev/v4l2_subdev# nodes. Keeping these open stops the underlying\n> hw-devices from being able to enter runtime-suspend causing significant\n> unnecessary power-usage.\n>\n> Add a stub acquireDevice() method to the PipelineHandler class which\n> pipeline handlers can override to delay opening /dev nodes until\n> the camera is acquired.\n>\n> Note pipeline handlers typically also will need access to /dev nodes\n> for their CameraConfig::validate() implementation for tryFormat() calls.\n> Making sure that /dev nodes are opened as necessary from validate() is\n> left up to the pipeline handler implementation.\n>\n> Signed-off-by: Hans de Goede \n> ---\n> include/libcamera/internal/pipeline_handler.h | 3 +-\n> src/libcamera/camera.cpp | 2 +-\n> src/libcamera/pipeline_handler.cpp | 43 +++++++++++++++----\n> 3 files changed, 37 insertions(+), 11 deletions(-)\n>\n> diff --git a/include/libcamera/internal/pipeline_handler.h\n> b/include/libcamera/internal/pipeline_handler.h\n> index cad5812f..597f7c3e 100644\n> --- a/include/libcamera/internal/pipeline_handler.h\n> +++ b/include/libcamera/internal/pipeline_handler.h\n> @@ -45,7 +45,7 @@ public:\n> MediaDevice *acquireMediaDevice(DeviceEnumerator *enumerator,\n> const DeviceMatch &dm);\n>\n> - bool acquire();\n> + bool acquire(Camera *camera);\n> void release(Camera *camera);\n>\n> virtual std::unique_ptr\n> generateConfiguration(Camera *camera,\n> @@ -79,6 +79,7 @@ protected:\n> virtual int queueRequestDevice(Camera *camera, Request *request) =\n> 0;\n> virtual void stopDevice(Camera *camera) = 0;\n>\n> + virtual bool acquireDevice(Camera *camera);\n> virtual void releaseDevice(Camera *camera);\n>\n> CameraManager *manager_;\n> diff --git a/src/libcamera/camera.cpp b/src/libcamera/camera.cpp\n> index 382a68f7..4e393f89 100644\n> --- a/src/libcamera/camera.cpp\n> +++ b/src/libcamera/camera.cpp\n> @@ -995,7 +995,7 @@ int Camera::acquire()\n> if (ret < 0)\n> return ret == -EACCES ? -EBUSY : ret;\n>\n> - if (!d->pipe_->acquire()) {\n> + if (!d->pipe_->acquire(this)) {\n> LOG(Camera, Info)\n> << \"Pipeline handler in use by another process\";\n> return -EBUSY;\n> diff --git a/src/libcamera/pipeline_handler.cpp\n> b/src/libcamera/pipeline_handler.cpp\n> index 1fc22d6a..e1342306 100644\n> --- a/src/libcamera/pipeline_handler.cpp\n> +++ b/src/libcamera/pipeline_handler.cpp\n> @@ -163,20 +163,22 @@ MediaDevice\n> *PipelineHandler::acquireMediaDevice(DeviceEnumerator *enumerator,\n> * has already acquired it\n> * \\sa release()\n> */\n> -bool PipelineHandler::acquire()\n> +bool PipelineHandler::acquire(Camera *camera)\n> {\n> MutexLocker locker(lock_);\n>\n> - if (useCount_) {\n> - ++useCount_;\n> - return true;\n> + if (useCount_ == 0) {\n> + for (std::shared_ptr &media : mediaDevices_) {\n> + if (!media->lock()) {\n> + unlockMediaDevices();\n> + return false;\n> + }\n> + }\n> }\n>\n> - for (std::shared_ptr &media : mediaDevices_) {\n> - if (!media->lock()) {\n> - unlockMediaDevices();\n> - return false;\n> - }\n> + if (!acquireDevice(camera)) {\n> + unlockMediaDevices();\n>\n\nI think we should only unlock media devices if it's the first acquire\nbeing called, as there might be other ongoing usages on other\ncameras [2]. Therefore:\n```\n if (useCount_ == 0)\n unlockMediaDevices();\n```\n\n[2]:\nhttps://chromium-review.googlesource.com/c/chromiumos/third_party/libcamera/+/5525900/7/src/libcamera/pipeline_handler.cpp#181\n\n+ return false;\n> }\n>\n> ++useCount_;\n> @@ -213,12 +215,35 @@ void PipelineHandler::release(Camera *camera)\n> --useCount_;\n> }\n>\n> +/**\n> + * \\brief Acquire resources associated with this camera\n> + * \\param[in] camera The camera for which to acquire resources\n> + *\n> + * Pipeline handlers may override this in order to get resources\n> + * such as open /dev nodes are allocate buffers when a camera is\n> + * acquired.\n> + *\n> + * Note this is called once for every camera which is acquired,\n> + * so if there are shared resources the pipeline handler must take\n> + * care to not release them until releaseDevice() has been called for\n> + * all previously acquired cameras.\n> + *\n> + * \\return True on success, false on failure.\n> + * \\sa releaseDevice()\n> + */\n> +bool PipelineHandler::acquireDevice([[maybe_unused]] Camera *camera)\n> +{\n> + return true;\n> +}\n> +\n> /**\n> * \\brief Release resources associated with this camera\n> * \\param[in] camera The camera for which to release resources\n> *\n> * Pipeline handlers may override this in order to perform cleanup\n> operations\n> * when a camera is released, such as freeing memory.\n> + *\n> + * \\sa acquireDevice()\n> */\n> void PipelineHandler::releaseDevice([[maybe_unused]] Camera *camera)\n> {\n> --\n> 2.46.0\n>\n>\nBR,\nHarvey","headers":{"Return-Path":"","X-Original-To":"parsemail@patchwork.libcamera.org","Delivered-To":"parsemail@patchwork.libcamera.org","Received":["from lancelot.ideasonboard.com (lancelot.ideasonboard.com\n\t[92.243.16.209])\n\tby patchwork.libcamera.org (Postfix) with ESMTPS id 4DA68BDE17\n\tfor ;\n\tWed, 21 Aug 2024 16:56:00 +0000 (UTC)","from lancelot.ideasonboard.com (localhost [IPv6:::1])\n\tby lancelot.ideasonboard.com (Postfix) with ESMTP id 2AF0A633CF;\n\tWed, 21 Aug 2024 18:55:59 +0200 (CEST)","from mail-lj1-x233.google.com (mail-lj1-x233.google.com\n\t[IPv6:2a00:1450:4864:20::233])\n\tby lancelot.ideasonboard.com (Postfix) with ESMTPS id 862F163394\n\tfor ;\n\tWed, 21 Aug 2024 18:55:57 +0200 (CEST)","by mail-lj1-x233.google.com with SMTP id\n\t38308e7fff4ca-2f3e071eb64so51326231fa.1\n\tfor ;\n\tWed, 21 Aug 2024 09:55:57 -0700 (PDT)"],"Authentication-Results":"lancelot.ideasonboard.com; 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boundary=\"000000000000706a1b0620346a74\"","X-BeenThere":"libcamera-devel@lists.libcamera.org","X-Mailman-Version":"2.1.29","Precedence":"list","List-Id":"","List-Unsubscribe":",\n\t","List-Archive":"","List-Post":"","List-Help":"","List-Subscribe":",\n\t","Errors-To":"libcamera-devel-bounces@lists.libcamera.org","Sender":"\"libcamera-devel\" "}},{"id":30893,"web_url":"https://patchwork.libcamera.org/comment/30893/","msgid":"<20240825004957.GB17238@pendragon.ideasonboard.com>","date":"2024-08-25T00:49:57","subject":"Re: [PATCH 3/5] pipeline_handler: Add acquireDevice() method to\n\tmirror existing releaseDevice()","submitter":{"id":2,"url":"https://patchwork.libcamera.org/api/people/2/","name":"Laurent Pinchart","email":"laurent.pinchart@ideasonboard.com"},"content":"On Wed, Aug 21, 2024 at 06:55:45PM +0200, Cheng-Hao Yang wrote:\n> Hi Hans,\n> \n> Thanks for the patch. Actually in mtkisp7, we did something very similar\n> [1].\n> (And I just caught a bug by checking your changes. Thanks :)\n> \n> [1]:\n> https://chromium-review.googlesource.com/c/chromiumos/third_party/libcamera/+/5525900\n> \n> On Tue, Aug 20, 2024 at 9:50 PM Hans de Goede wrote:\n> \n> > ATM libcamera always keeps all /dev/video# and /dev/v4l2_subdev# nodes\n> > for a pipeline open after enumerating the camera.\n> >\n> > This is a problem for uvcvideo and atomisp /dev/video# nodes as well as\n> > for VCM /dev/v4l2_subdev# nodes. Keeping these open stops the underlying\n> > hw-devices from being able to enter runtime-suspend causing significant\n> > unnecessary power-usage.\n> >\n> > Add a stub acquireDevice() method to the PipelineHandler class which\n> > pipeline handlers can override to delay opening /dev nodes until\n> > the camera is acquired.\n> >\n> > Note pipeline handlers typically also will need access to /dev nodes\n> > for their CameraConfig::validate() implementation for tryFormat() calls.\n> > Making sure that /dev nodes are opened as necessary from validate() is\n> > left up to the pipeline handler implementation.\n> >\n> > Signed-off-by: Hans de Goede \n> > ---\n> > include/libcamera/internal/pipeline_handler.h | 3 +-\n> > src/libcamera/camera.cpp | 2 +-\n> > src/libcamera/pipeline_handler.cpp | 43 +++++++++++++++----\n> > 3 files changed, 37 insertions(+), 11 deletions(-)\n> >\n> > diff --git a/include/libcamera/internal/pipeline_handler.h\n> > b/include/libcamera/internal/pipeline_handler.h\n> > index cad5812f..597f7c3e 100644\n> > --- a/include/libcamera/internal/pipeline_handler.h\n> > +++ b/include/libcamera/internal/pipeline_handler.h\n> > @@ -45,7 +45,7 @@ public:\n> > MediaDevice *acquireMediaDevice(DeviceEnumerator *enumerator,\n> > const DeviceMatch &dm);\n> >\n> > - bool acquire();\n> > + bool acquire(Camera *camera);\n> > void release(Camera *camera);\n> >\n> > virtual std::unique_ptr\n> > generateConfiguration(Camera *camera,\n> > @@ -79,6 +79,7 @@ protected:\n> > virtual int queueRequestDevice(Camera *camera, Request *request) =\n> > 0;\n> > virtual void stopDevice(Camera *camera) = 0;\n> >\n> > + virtual bool acquireDevice(Camera *camera);\n> > virtual void releaseDevice(Camera *camera);\n> >\n> > CameraManager *manager_;\n> > diff --git a/src/libcamera/camera.cpp b/src/libcamera/camera.cpp\n> > index 382a68f7..4e393f89 100644\n> > --- a/src/libcamera/camera.cpp\n> > +++ b/src/libcamera/camera.cpp\n> > @@ -995,7 +995,7 @@ int Camera::acquire()\n> > if (ret < 0)\n> > return ret == -EACCES ? -EBUSY : ret;\n> >\n> > - if (!d->pipe_->acquire()) {\n> > + if (!d->pipe_->acquire(this)) {\n> > LOG(Camera, Info)\n> > << \"Pipeline handler in use by another process\";\n> > return -EBUSY;\n> > diff --git a/src/libcamera/pipeline_handler.cpp\n> > b/src/libcamera/pipeline_handler.cpp\n> > index 1fc22d6a..e1342306 100644\n> > --- a/src/libcamera/pipeline_handler.cpp\n> > +++ b/src/libcamera/pipeline_handler.cpp\n> > @@ -163,20 +163,22 @@ MediaDevice\n> > *PipelineHandler::acquireMediaDevice(DeviceEnumerator *enumerator,\n> > * has already acquired it\n> > * \\sa release()\n> > */\n> > -bool PipelineHandler::acquire()\n> > +bool PipelineHandler::acquire(Camera *camera)\n> > {\n> > MutexLocker locker(lock_);\n> >\n> > - if (useCount_) {\n> > - ++useCount_;\n> > - return true;\n> > + if (useCount_ == 0) {\n> > + for (std::shared_ptr &media : mediaDevices_) {\n> > + if (!media->lock()) {\n> > + unlockMediaDevices();\n> > + return false;\n> > + }\n> > + }\n> > }\n> >\n> > - for (std::shared_ptr &media : mediaDevices_) {\n> > - if (!media->lock()) {\n> > - unlockMediaDevices();\n> > - return false;\n> > - }\n> > + if (!acquireDevice(camera)) {\n> > + unlockMediaDevices();\n> >\n> \n> I think we should only unlock media devices if it's the first acquire\n> being called, as there might be other ongoing usages on other\n> cameras [2]. Therefore:\n> ```\n> if (useCount_ == 0)\n> unlockMediaDevices();\n> ```\n> \n> [2]:\n> https://chromium-review.googlesource.com/c/chromiumos/third_party/libcamera/+/5525900/7/src/libcamera/pipeline_handler.cpp#181\n> \n> + return false;\n> > }\n> >\n> > ++useCount_;\n> > @@ -213,12 +215,35 @@ void PipelineHandler::release(Camera *camera)\n> > --useCount_;\n> > }\n> >\n> > +/**\n> > + * \\brief Acquire resources associated with this camera\n> > + * \\param[in] camera The camera for which to acquire resources\n> > + *\n> > + * Pipeline handlers may override this in order to get resources\n> > + * such as open /dev nodes are allocate buffers when a camera is\n\ns@open /dev nodes@opening devices/\ns/are allocate/and allocating/\n\nAs discussed previously, I think we need to improve the\napplication-facing API to make resource and power management more\nexplicit. Camera::acquire() was never meant for this purpose. I\nunderstand we need a short term solution to the power consumption issue\nfor UVC cameras without an enormous amount of yak shaving, and I'm fine\nwith this patch series as an interim measure, but I don't want to see\nacquireDevice() being used in random ways by pipeline handlers other\nthan UVC before we address the more general problem. This should be\ndocumented here.\n\n> > + * acquired.\n\nPlease reflow these paragraphs to 80 columns.\n\n> > + *\n> > + * Note this is called once for every camera which is acquired,\n\ns/which/that/\n\n> > + * so if there are shared resources the pipeline handler must take\n\ns/shared resources/resources shared by multiple cameras/\n\n> > + * care to not release them until releaseDevice() has been called for\n> > + * all previously acquired cameras.\n\nDoesn't this paragraph belong to releaseDevice() ?\n\n> > + *\n> > + * \\return True on success, false on failure.\n> > + * \\sa releaseDevice()\n> > + */\n> > +bool PipelineHandler::acquireDevice([[maybe_unused]] Camera *camera)\n> > +{\n> > + return true;\n> > +}\n> > +\n> > /**\n> > * \\brief Release resources associated with this camera\n> > * \\param[in] camera The camera for which to release resources\n> > *\n> > * Pipeline handlers may override this in order to perform cleanup\n> > operations\n> > * when a camera is released, such as freeing memory.\n> > + *\n> > + * \\sa acquireDevice()\n> > */\n> > void PipelineHandler::releaseDevice([[maybe_unused]] Camera *camera)\n> > {","headers":{"Return-Path":"","X-Original-To":"parsemail@patchwork.libcamera.org","Delivered-To":"parsemail@patchwork.libcamera.org","Received":["from lancelot.ideasonboard.com (lancelot.ideasonboard.com\n\t[92.243.16.209])\n\tby patchwork.libcamera.org (Postfix) with ESMTPS id DCD0CBDE17\n\tfor ;\n\tSun, 25 Aug 2024 00:50:04 +0000 (UTC)","from lancelot.ideasonboard.com (localhost [IPv6:::1])\n\tby lancelot.ideasonboard.com (Postfix) with ESMTP id EEB8E633CF;\n\tSun, 25 Aug 2024 02:50:03 +0200 (CEST)","from perceval.ideasonboard.com (perceval.ideasonboard.com\n\t[IPv6:2001:4b98:dc2:55:216:3eff:fef7:d647])\n\tby lancelot.ideasonboard.com (Postfix) with ESMTPS id 16D2E61902\n\tfor ;\n\tSun, 25 Aug 2024 02:50:02 +0200 (CEST)","from pendragon.ideasonboard.com (81-175-209-231.bb.dnainternet.fi\n\t[81.175.209.231])\n\tby perceval.ideasonboard.com (Postfix) with ESMTPSA id 9856D480;\n\tSun, 25 Aug 2024 02:48:56 +0200 (CEST)"],"Authentication-Results":"lancelot.ideasonboard.com; dkim=pass (1024-bit key;\n\tunprotected) header.d=ideasonboard.com header.i=@ideasonboard.com\n\theader.b=\"UxJ9ftLw\"; dkim-atps=neutral","DKIM-Signature":"v=1; a=rsa-sha256; c=relaxed/simple; d=ideasonboard.com;\n\ts=mail; t=1724546936;\n\tbh=Xy6VDPPV5cP/MYVrfReJPx5ojAgNar98jRSlIeaiCfo=;\n\th=Date:From:To:Cc:Subject:References:In-Reply-To:From;\n\tb=UxJ9ftLw2LlfEAVsewvYXYPzzWDAoQMeE9lKUOTf7Bv6iP8gafhOIOsiOHZMCxHHs\n\t+irjRIdhU27xR4T/mVsXvy6Q7geLM3PhtdkxIad4dPtLsCNDhVl2R9C1VL8OI4uCqb\n\tPlsPUTBFrDe49AkjJ4RsoVtm4YZqNv+UC5ESgkwg=","Date":"Sun, 25 Aug 2024 03:49:57 +0300","From":"Laurent Pinchart ","To":"Cheng-Hao Yang ","Cc":"Hans de Goede , libcamera-devel@lists.libcamera.org,\n\tMaxime Ripard , Milan Zamazal ","Subject":"Re: [PATCH 3/5] pipeline_handler: Add acquireDevice() method to\n\tmirror existing releaseDevice()","Message-ID":"<20240825004957.GB17238@pendragon.ideasonboard.com>","References":"<20240820195016.16028-1-hdegoede@redhat.com>\n\t<20240820195016.16028-4-hdegoede@redhat.com>\n\t","MIME-Version":"1.0","Content-Type":"text/plain; charset=utf-8","Content-Disposition":"inline","Content-Transfer-Encoding":"8bit","In-Reply-To":"","X-BeenThere":"libcamera-devel@lists.libcamera.org","X-Mailman-Version":"2.1.29","Precedence":"list","List-Id":"","List-Unsubscribe":",\n\t","List-Archive":"","List-Post":"","List-Help":"","List-Subscribe":",\n\t","Errors-To":"libcamera-devel-bounces@lists.libcamera.org","Sender":"\"libcamera-devel\" "}},{"id":30922,"web_url":"https://patchwork.libcamera.org/comment/30922/","msgid":"<79188a4f-0409-4581-869f-07aa20d94110@redhat.com>","date":"2024-08-27T14:11:47","subject":"Re: [PATCH 3/5] pipeline_handler: Add acquireDevice() method to\n\tmirror existing releaseDevice()","submitter":{"id":102,"url":"https://patchwork.libcamera.org/api/people/102/","name":"Hans de Goede","email":"hdegoede@redhat.com"},"content":"Hi,\n\nOn 8/21/24 6:55 PM, Cheng-Hao Yang wrote:\n> Hi Hans,\n> \n> Thanks for the patch. Actually in mtkisp7, we did something very similar [1].\n> (And I just caught a bug by checking your changes. Thanks :)\n> \n> [1]: https://chromium-review.googlesource.com/c/chromiumos/third_party/libcamera/+/5525900 \n> \n> On Tue, Aug 20, 2024 at 9:50 PM Hans de Goede > wrote:\n> \n> ATM libcamera always keeps all /dev/video# and /dev/v4l2_subdev# nodes\n> for a pipeline open after enumerating the camera.\n> \n> This is a problem for uvcvideo and atomisp /dev/video# nodes as well as\n> for VCM /dev/v4l2_subdev# nodes. Keeping these open stops the underlying\n> hw-devices from being able to enter runtime-suspend causing significant\n> unnecessary power-usage.\n> \n> Add a stub acquireDevice() method to the PipelineHandler class which\n> pipeline handlers can override to delay opening /dev nodes until\n> the camera is acquired.\n> \n> Note pipeline handlers typically also will need access to /dev nodes\n> for their CameraConfig::validate() implementation for tryFormat() calls.\n> Making sure that /dev nodes are opened as necessary from validate() is\n> left up to the pipeline handler implementation.\n> \n> Signed-off-by: Hans de Goede >\n> ---\n>  include/libcamera/internal/pipeline_handler.h |  3 +-\n>  src/libcamera/camera.cpp                      |  2 +-\n>  src/libcamera/pipeline_handler.cpp            | 43 +++++++++++++++----\n>  3 files changed, 37 insertions(+), 11 deletions(-)\n> \n> diff --git a/include/libcamera/internal/pipeline_handler.h b/include/libcamera/internal/pipeline_handler.h\n> index cad5812f..597f7c3e 100644\n> --- a/include/libcamera/internal/pipeline_handler.h\n> +++ b/include/libcamera/internal/pipeline_handler.h\n> @@ -45,7 +45,7 @@ public:\n>         MediaDevice *acquireMediaDevice(DeviceEnumerator *enumerator,\n>                                         const DeviceMatch &dm);\n> \n> -       bool acquire();\n> +       bool acquire(Camera *camera);\n>         void release(Camera *camera);\n> \n>         virtual std::unique_ptr generateConfiguration(Camera *camera,\n> @@ -79,6 +79,7 @@ protected:\n>         virtual int queueRequestDevice(Camera *camera, Request *request) = 0;\n>         virtual void stopDevice(Camera *camera) = 0;\n> \n> +       virtual bool acquireDevice(Camera *camera);\n>         virtual void releaseDevice(Camera *camera);\n> \n>         CameraManager *manager_;\n> diff --git a/src/libcamera/camera.cpp b/src/libcamera/camera.cpp\n> index 382a68f7..4e393f89 100644\n> --- a/src/libcamera/camera.cpp\n> +++ b/src/libcamera/camera.cpp\n> @@ -995,7 +995,7 @@ int Camera::acquire()\n>         if (ret < 0)\n>                 return ret == -EACCES ? -EBUSY : ret;\n> \n> -       if (!d->pipe_->acquire()) {\n> +       if (!d->pipe_->acquire(this)) {\n>                 LOG(Camera, Info)\n>                         << \"Pipeline handler in use by another process\";\n>                 return -EBUSY;\n> diff --git a/src/libcamera/pipeline_handler.cpp b/src/libcamera/pipeline_handler.cpp\n> index 1fc22d6a..e1342306 100644\n> --- a/src/libcamera/pipeline_handler.cpp\n> +++ b/src/libcamera/pipeline_handler.cpp\n> @@ -163,20 +163,22 @@ MediaDevice *PipelineHandler::acquireMediaDevice(DeviceEnumerator *enumerator,\n>   * has already acquired it\n>   * \\sa release()\n>   */\n> -bool PipelineHandler::acquire()\n> +bool PipelineHandler::acquire(Camera *camera)\n>  {\n>         MutexLocker locker(lock_);\n> \n> -       if (useCount_) {\n> -               ++useCount_;\n> -               return true;\n> +       if (useCount_ == 0) {\n> +               for (std::shared_ptr &media : mediaDevices_) {\n> +                       if (!media->lock()) {\n> +                               unlockMediaDevices();\n> +                               return false;\n> +                       }\n> +               }\n>         }\n> \n> -       for (std::shared_ptr &media : mediaDevices_) {\n> -               if (!media->lock()) {\n> -                       unlockMediaDevices();\n> -                       return false;\n> -               }\n> +       if (!acquireDevice(camera)) {\n> +               unlockMediaDevices();\n> \n>  \n> I think we should only unlock media devices if it's the first acquire\n> being called, as there might be other ongoing usages on other\n> cameras [2]. Therefore:\n> ```\n>                     if (useCount_ == 0)\n>                             unlockMediaDevices();\n> ```\n\nGood point, fixed for v2.\n\nRegards,\n\nHans","headers":{"Return-Path":"","X-Original-To":"parsemail@patchwork.libcamera.org","Delivered-To":"parsemail@patchwork.libcamera.org","Received":["from lancelot.ideasonboard.com (lancelot.ideasonboard.com\n\t[92.243.16.209])\n\tby patchwork.libcamera.org (Postfix) with ESMTPS id EB7A2C323E\n\tfor ;\n\tTue, 27 Aug 2024 14:11:55 +0000 (UTC)","from lancelot.ideasonboard.com (localhost [IPv6:::1])\n\tby lancelot.ideasonboard.com (Postfix) with ESMTP id E531D63460;\n\tTue, 27 Aug 2024 16:11:54 +0200 (CEST)","from us-smtp-delivery-124.mimecast.com\n\t(us-smtp-delivery-124.mimecast.com [170.10.133.124])\n\tby lancelot.ideasonboard.com (Postfix) with ESMTPS id A054961901\n\tfor ;\n\tTue, 27 Aug 2024 16:11:53 +0200 (CEST)","from mail-lj1-f197.google.com (mail-lj1-f197.google.com\n\t[209.85.208.197]) by relay.mimecast.com with ESMTP with STARTTLS\n\t(version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id\n\tus-mta-160-y2FB4cIMPC-f6eqiCYG2NQ-1; 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\n\tTue, 27 Aug 2024 07:11:48 -0700 (PDT)","by 2002:a2e:bc17:0:b0:2f5:966:c22e with SMTP id\n\t38308e7fff4ca-2f50966c499mr67598961fa.11.1724767907979; \n\tTue, 27 Aug 2024 07:11:47 -0700 (PDT)"],"X-Google-Smtp-Source":"AGHT+IELBAsQUDkUYdgIyHwefV93RYc3KsL9Nu1w/2o43bJWeip81uZM+km/cFG5khEDxXJLGVYTSw==","Message-ID":"<79188a4f-0409-4581-869f-07aa20d94110@redhat.com>","Date":"Tue, 27 Aug 2024 16:11:47 +0200","MIME-Version":"1.0","User-Agent":"Mozilla Thunderbird","Subject":"Re: [PATCH 3/5] pipeline_handler: Add acquireDevice() method to\n\tmirror existing releaseDevice()","To":"Cheng-Hao Yang ","Cc":"libcamera-devel@lists.libcamera.org, Maxime Ripard , \n\tMilan Zamazal ","References":"<20240820195016.16028-1-hdegoede@redhat.com>\n\t<20240820195016.16028-4-hdegoede@redhat.com>\n\t","From":"Hans de Goede ","In-Reply-To":"","X-Mimecast-Spam-Score":"0","X-Mimecast-Originator":"redhat.com","Content-Language":"en-US, nl","Content-Type":"text/plain; charset=UTF-8","Content-Transfer-Encoding":"8bit","X-BeenThere":"libcamera-devel@lists.libcamera.org","X-Mailman-Version":"2.1.29","Precedence":"list","List-Id":"","List-Unsubscribe":",\n\t","List-Archive":"","List-Post":"","List-Help":"","List-Subscribe":",\n\t","Errors-To":"libcamera-devel-bounces@lists.libcamera.org","Sender":"\"libcamera-devel\" "}},{"id":30924,"web_url":"https://patchwork.libcamera.org/comment/30924/","msgid":"","date":"2024-08-27T14:25:00","subject":"Re: [PATCH 3/5] pipeline_handler: Add acquireDevice() method to\n\tmirror existing releaseDevice()","submitter":{"id":102,"url":"https://patchwork.libcamera.org/api/people/102/","name":"Hans de Goede","email":"hdegoede@redhat.com"},"content":"Hi,\n\nOn 8/25/24 2:49 AM, Laurent Pinchart wrote:\n\n\n\n>>> @@ -213,12 +215,35 @@ void PipelineHandler::release(Camera *camera)\n>>> --useCount_;\n>>> }\n>>>\n>>> +/**\n>>> + * \\brief Acquire resources associated with this camera\n>>> + * \\param[in] camera The camera for which to acquire resources\n>>> + *\n>>> + * Pipeline handlers may override this in order to get resources\n>>> + * such as open /dev nodes are allocate buffers when a camera is\n> \n> s@open /dev nodes@opening devices/\n> s/are allocate/and allocating/\n\nAck, fixed for v2.\n\n> As discussed previously, I think we need to improve the\n> application-facing API to make resource and power management more\n> explicit. Camera::acquire() was never meant for this purpose. I\n> understand we need a short term solution to the power consumption issue\n> for UVC cameras without an enormous amount of yak shaving\n\nAck, I have posted a RFC with the application-facing API changes we discussed\nfor this:\n\nhttps://lists.libcamera.org/pipermail/libcamera-devel/2024-August/044384.html\n\n> and I'm fine\n> with this patch series as an interim measure, but I don't want to see\n> acquireDevice() being used in random ways by pipeline handlers other\n> than UVC before we address the more general problem. This should be\n> documented here.\n\nOk I have added the following block to the docbook comment to address\nthis for v2:\n\n * This is used by the uvcvideo pipeline handler to delay opening /dev/video#\n * until the camera is acquired to avoid excess power consumption. The delayed\n * opening of /dev/video# is a special case because the kernel uvcvideo driver\n * powers on the USB device as soon as /dev/video# is opened. This behavior\n * must *not* be copied by other drivers.\n\n>>> + * acquired.\n> \n> Please reflow these paragraphs to 80 columns.\n\nAck, done for v2.\n\n> \n>>> + *\n>>> + * Note this is called once for every camera which is acquired,\n> \n> s/which/that/\n> \n>>> + * so if there are shared resources the pipeline handler must take\n> \n> s/shared resources/resources shared by multiple cameras/\n> \n>>> + * care to not release them until releaseDevice() has been called for\n>>> + * all previously acquired cameras.\n> \n> Doesn't this paragraph belong to releaseDevice() ?\n\nthat is a better place yes, I have moved it for v2.\n\nRegards,\n\nHans","headers":{"Return-Path":"","X-Original-To":"parsemail@patchwork.libcamera.org","Delivered-To":"parsemail@patchwork.libcamera.org","Received":["from lancelot.ideasonboard.com (lancelot.ideasonboard.com\n\t[92.243.16.209])\n\tby patchwork.libcamera.org (Postfix) with ESMTPS id A9AF2C324C\n\tfor ;\n\tTue, 27 Aug 2024 14:25:08 +0000 (UTC)","from lancelot.ideasonboard.com (localhost [IPv6:::1])\n\tby lancelot.ideasonboard.com (Postfix) with ESMTP id A6DBD63461;\n\tTue, 27 Aug 2024 16:25:07 +0200 (CEST)","from us-smtp-delivery-124.mimecast.com\n\t(us-smtp-delivery-124.mimecast.com [170.10.133.124])\n\tby lancelot.ideasonboard.com (Postfix) with ESMTPS id 52A2D61901\n\tfor ;\n\tTue, 27 Aug 2024 16:25:06 +0200 (CEST)","from mail-lf1-f69.google.com (mail-lf1-f69.google.com\n\t[209.85.167.69]) by relay.mimecast.com with ESMTP with STARTTLS\n\t(version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id\n\tus-mta-396-bQrP9I-nMJuwD3cBaZ2tMQ-1; 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\n\tTue, 27 Aug 2024 07:25:01 -0700 (PDT)","by 2002:a05:6512:1596:b0:52c:deb9:904b with SMTP id\n\t2adb3069b0e04-5343887e17bmr12093812e87.38.1724768701402; \n\tTue, 27 Aug 2024 07:25:01 -0700 (PDT)"],"X-Google-Smtp-Source":"AGHT+IFWFHD/U9MYIZxia6mp3q4ktTAecXnMEpfYjQwHrglh/rR0goMwoX11bOlkm7VUTDL4Q4IHjA==","Message-ID":"","Date":"Tue, 27 Aug 2024 16:25:00 +0200","MIME-Version":"1.0","User-Agent":"Mozilla Thunderbird","Subject":"Re: [PATCH 3/5] pipeline_handler: Add acquireDevice() method to\n\tmirror existing releaseDevice()","To":"Laurent Pinchart ,\n\tCheng-Hao Yang ","Cc":"libcamera-devel@lists.libcamera.org, Maxime Ripard , \n\tMilan Zamazal ","References":"<20240820195016.16028-1-hdegoede@redhat.com>\n\t<20240820195016.16028-4-hdegoede@redhat.com>\n\t\n\t<20240825004957.GB17238@pendragon.ideasonboard.com>","From":"Hans de Goede ","In-Reply-To":"<20240825004957.GB17238@pendragon.ideasonboard.com>","X-Mimecast-Spam-Score":"0","X-Mimecast-Originator":"redhat.com","Content-Language":"en-US, nl","Content-Type":"text/plain; charset=UTF-8","Content-Transfer-Encoding":"7bit","X-BeenThere":"libcamera-devel@lists.libcamera.org","X-Mailman-Version":"2.1.29","Precedence":"list","List-Id":"","List-Unsubscribe":",\n\t","List-Archive":"","List-Post":"","List-Help":"","List-Subscribe":",\n\t","Errors-To":"libcamera-devel-bounces@lists.libcamera.org","Sender":"\"libcamera-devel\" "}},{"id":30963,"web_url":"https://patchwork.libcamera.org/comment/30963/","msgid":"<20240829210631.GF15799@pendragon.ideasonboard.com>","date":"2024-08-29T21:06:31","subject":"Re: [PATCH 3/5] pipeline_handler: Add acquireDevice() method to\n\tmirror existing releaseDevice()","submitter":{"id":2,"url":"https://patchwork.libcamera.org/api/people/2/","name":"Laurent Pinchart","email":"laurent.pinchart@ideasonboard.com"},"content":"Hi Hans,\n\nOn Tue, Aug 27, 2024 at 04:25:00PM +0200, Hans de Goede wrote:\n> On 8/25/24 2:49 AM, Laurent Pinchart wrote:\n> \n> \n> \n> >>> @@ -213,12 +215,35 @@ void PipelineHandler::release(Camera *camera)\n> >>> --useCount_;\n> >>> }\n> >>>\n> >>> +/**\n> >>> + * \\brief Acquire resources associated with this camera\n> >>> + * \\param[in] camera The camera for which to acquire resources\n> >>> + *\n> >>> + * Pipeline handlers may override this in order to get resources\n> >>> + * such as open /dev nodes are allocate buffers when a camera is\n> > \n> > s@open /dev nodes@opening devices/\n> > s/are allocate/and allocating/\n> \n> Ack, fixed for v2.\n> \n> > As discussed previously, I think we need to improve the\n> > application-facing API to make resource and power management more\n> > explicit. Camera::acquire() was never meant for this purpose. I\n> > understand we need a short term solution to the power consumption issue\n> > for UVC cameras without an enormous amount of yak shaving\n> \n> Ack, I have posted a RFC with the application-facing API changes we discussed\n> for this:\n> \n> https://lists.libcamera.org/pipermail/libcamera-devel/2024-August/044384.html\n\nThank you for that. I really appreciate your efforts. I'll reply to the\nRFC after reviewing v2 of this series.\n\n> > and I'm fine\n> > with this patch series as an interim measure, but I don't want to see\n> > acquireDevice() being used in random ways by pipeline handlers other\n> > than UVC before we address the more general problem. This should be\n> > documented here.\n> \n> Ok I have added the following block to the docbook comment to address\n> this for v2:\n> \n> * This is used by the uvcvideo pipeline handler to delay opening /dev/video#\n> * until the camera is acquired to avoid excess power consumption. The delayed\n> * opening of /dev/video# is a special case because the kernel uvcvideo driver\n> * powers on the USB device as soon as /dev/video# is opened. This behavior\n> * must *not* be copied by other drivers.\n> \n> >>> + * acquired.\n> > \n> > Please reflow these paragraphs to 80 columns.\n> \n> Ack, done for v2.\n> \n> >>> + *\n> >>> + * Note this is called once for every camera which is acquired,\n> > \n> > s/which/that/\n> > \n> >>> + * so if there are shared resources the pipeline handler must take\n> > \n> > s/shared resources/resources shared by multiple cameras/\n> > \n> >>> + * care to not release them until releaseDevice() has been called for\n> >>> + * all previously acquired cameras.\n> > \n> > Doesn't this paragraph belong to releaseDevice() ?\n> \n> that is a better place yes, I have moved it for v2.","headers":{"Return-Path":"","X-Original-To":"parsemail@patchwork.libcamera.org","Delivered-To":"parsemail@patchwork.libcamera.org","Received":["from lancelot.ideasonboard.com (lancelot.ideasonboard.com\n\t[92.243.16.209])\n\tby patchwork.libcamera.org (Postfix) with ESMTPS id 7C97AC324C\n\tfor ;\n\tThu, 29 Aug 2024 21:07:06 +0000 (UTC)","from lancelot.ideasonboard.com (localhost [IPv6:::1])\n\tby lancelot.ideasonboard.com (Postfix) with ESMTP id 688C063469;\n\tThu, 29 Aug 2024 23:07:05 +0200 (CEST)","from perceval.ideasonboard.com (perceval.ideasonboard.com\n\t[IPv6:2001:4b98:dc2:55:216:3eff:fef7:d647])\n\tby lancelot.ideasonboard.com (Postfix) with ESMTPS id BC6F463456\n\tfor ;\n\tThu, 29 Aug 2024 23:07:03 +0200 (CEST)","from pendragon.ideasonboard.com (81-175-209-231.bb.dnainternet.fi\n\t[81.175.209.231])\n\tby perceval.ideasonboard.com (Postfix) with ESMTPSA id DD9E4226;\n\tThu, 29 Aug 2024 23:05:54 +0200 (CEST)"],"Authentication-Results":"lancelot.ideasonboard.com; dkim=pass (1024-bit key;\n\tunprotected) header.d=ideasonboard.com header.i=@ideasonboard.com\n\theader.b=\"wbaXYpeu\"; dkim-atps=neutral","DKIM-Signature":"v=1; a=rsa-sha256; c=relaxed/simple; d=ideasonboard.com;\n\ts=mail; t=1724965555;\n\tbh=FvU9ylIYkzbOFIYIa9xqF2vEM4AWFOX8n+sIYFPuMiM=;\n\th=Date:From:To:Cc:Subject:References:In-Reply-To:From;\n\tb=wbaXYpeuWijW8HY12e1qkC36R6VHEDd2bAHsY0jn+OvU5VExjnN8IhghIeYpR7LAW\n\taZAcMS3DQthZKH0edI5eht8nLCUJaCPkQUc8F2M3lJmIJHIgz2SjCl3I4jOO6NIPXU\n\tnPjDh1iTdGge5SuxnuuolqD7ROhLZn5CIMZi0hzc=","Date":"Fri, 30 Aug 2024 00:06:31 +0300","From":"Laurent Pinchart ","To":"Hans de Goede ","Cc":"Cheng-Hao Yang ,\n\tlibcamera-devel@lists.libcamera.org, Maxime Ripard , \n\tMilan Zamazal ","Subject":"Re: [PATCH 3/5] pipeline_handler: Add acquireDevice() method to\n\tmirror existing releaseDevice()","Message-ID":"<20240829210631.GF15799@pendragon.ideasonboard.com>","References":"<20240820195016.16028-1-hdegoede@redhat.com>\n\t<20240820195016.16028-4-hdegoede@redhat.com>\n\t\n\t<20240825004957.GB17238@pendragon.ideasonboard.com>\n\t","MIME-Version":"1.0","Content-Type":"text/plain; charset=utf-8","Content-Disposition":"inline","In-Reply-To":"","X-BeenThere":"libcamera-devel@lists.libcamera.org","X-Mailman-Version":"2.1.29","Precedence":"list","List-Id":"","List-Unsubscribe":",\n\t","List-Archive":"","List-Post":"","List-Help":"","List-Subscribe":",\n\t","Errors-To":"libcamera-devel-bounces@lists.libcamera.org","Sender":"\"libcamera-devel\" "}}]