Message-ID: <20241110150859.GC6002@pendragon.ideasonboard.com>
Date: Sun, 10 Nov 2024 17:08:59 +0200
From: Laurent Pinchart <laurent.pinchart@...asonboard.com>
To: Hans de Goede <hdegoede@...hat.com>
Cc: Ricardo Ribalda <ribalda@...omium.org>,
	Mauro Carvalho Chehab <mchehab@...nel.org>,
	Sakari Ailus <sakari.ailus@...ux.intel.com>,
	linux-kernel@...r.kernel.org, linux-media@...r.kernel.org,
	Yunke Cao <yunkec@...omium.org>, Hans Verkuil <hverkuil@...all.nl>
Subject: Re: [PATCH v2 0/6] media: uvcvideo: Implement the Privacy GPIO as a
 subdevice

On Sat, Nov 09, 2024 at 04:37:10PM +0100, Hans de Goede wrote:
> Hi Ricardo,
> 
> FYI / some background: I have been asked to start helping /
> co-maintaining UVC with Laurent. I'll send out a patch adding
> myself as UVC maintainer soon.
> 
> On 8-Nov-24 9:25 PM, Ricardo Ribalda wrote:
> > Some notebooks have a button to disable the camera (not to be mistaken
> > with the mechanical cover). This is a standard GPIO linked to the
> > camera via the ACPI table.
> > 
> > 4 years ago we added support for this button in UVC via the Privacy control.
> > This has two issues:
> > - If the camera has its own privacy control, it will be masked
> > - We need to power-up the camera to read the privacy control gpio.
> > 
> > We tried to fix the power-up issues implementing "granular power
> > saving" but it has been more complicated than anticipated....
> 
> I have been discussing UVC power-management with Laurent, also
> related to power-consumption issues caused by libcamera's pipeline
> handler holding open the /dev/video# node as long as the camera
> manager object exists.
> 
> For now we have fixed this with some relatively small changes to
> libcamera's uvcvideo pipeline handler, but that is really meant
> as an interim solution and as this privacy control series shows
> the power-management issues are real.
> 
> Combined with Mauro's remarks about how this is an userspace ABI break (1)
> I think we should maybe first take another look at the powermanagement
> issues in general rather then moving forward with this series.
> 
> My apologies for this, I realize how annoying it can be when you are
> working on a patch series to fix a specific issue and a reviewer
> moves the goal-posts like this. But I do really think that just fixing
> the generic power-management issues would be better and I also think
> that this should be feasible / not too hard.
> 
> Here is what I have in mind for this:
> 
> 1. Assume that the results of trying a specific fmt do not change over time.
> 
> 2. Only allow userspace to request fmts which match one of the enum-fmts ->
>    enum-frame-sizes -> enum-frame-rates tripplet results
>    (constrain what userspace requests to these)
> 
> 3. Run the equivalent of tryfmt on all possible combinations (so the usaul
>    3 levels nested loop for this) on probe() and cache the results

This is possibly problematic. If I recall correctly (it was a very long
time ago), the gstreamer v4l2src element used to do this, and it
resulted in very large delays (> 10s with some devices), and possibly in
some devices crashing as well.

> 4. Make try_fmt / set_fmt not poweron the device but instead constrain
>    the requested fmt to one from our cached fmts
> 
> 5. On stream-on do the actual power-on + set-fmt + verify that we get
>    what we expect based on the cache, and otherwise return -EIO.
> 
> I think that should sort the issue, assuming that 1. above holds true.
> 
> One downside is that this stops UVC button presses from working when
> not streaming. But userspace will typically only open the /dev/video#
> node if it plans to stream anyways so there should not be much of
> a difference wrt button press behavior.
> 
> This should also make camera enumeration faster for apps, since
> most apps / frameworks do the whole 3 levels nested loop for this
> on startup, for which atm we go out to the hw, which now instead
> will come from the fmts cache and thus will be much much faster,
> so this should lead to a noticeable speedup for apps accessing UVC
> cameras which would be another nice win.
> 
> Downside is that the initial probe will take longer see we do
> all the tryfmt-s there now. But I think that taking a bit longer
> to probe while the machine is booting should not be an issue.

It depends on how much "a bit" is. I don't think a >10s delay would be
acceptable.

> 1) Which is technically correct, but FWIW I agree with you that I think
> most userspace consumers will not care
> 
> > Last year, we proposed a patchset to implement the privacy gpio as a
> > subdevice https://lore.kernel.org/linux-media/20230111-uvc_privacy_subdev-v1-0-f859ac9a01e3@chromium.org/
> > 
> > I think it is a pretty clean solution and makes sense to use a
> > subdevice for something that is a sub device of the camera :).
> > 
> > This is an attempt to continue with that approach.
> > 
> > Tested on gimble:
> > gimble-rev3 ~ # v4l2-ctl --all -d /dev/v4l-subdev0
> > Driver Info:
> >         Driver version   : 6.6.56
> >         Capabilities     : 0x00000000
> > Media Driver Info:
> >         Driver name      : uvcvideo
> >         Model            : HP 5M Camera: HP 5M Camera
> >         Serial           : 0001
> >         Bus info         : usb-0000:00:14.0-6
> >         Media version    : 6.6.56
> >         Hardware revision: 0x00009601 (38401)
> >         Driver version   : 6.6.56
> > Interface Info:
> >         ID               : 0x0300001d
> >         Type             : V4L Sub-Device
> > Entity Info:
> >         ID               : 0x00000013 (19)
> >         Name             : GPIO
> >         Function         : Unknown sub-device (00020006)
> > 
> > Camera Controls
> > 
> >                         privacy 0x009a0910 (bool)   : default=0 value=0 flags=read-only, volatile
> > 
> > gimble-rev3 ~ # media-ctl  -p
> > Media controller API version 6.6.56
> > 
> > Media device information
> > ------------------------
> > driver          uvcvideo
> > model           HP 5M Camera: HP 5M Camera
> > serial          0001
> > bus info        usb-0000:00:14.0-6
> > hw revision     0x9601
> > driver version  6.6.56
> > 
> > Device topology
> > - entity 1: HP 5M Camera: HP 5M Camera (1 pad, 1 link)
> >             type Node subtype V4L flags 1
> >             device node name /dev/video0
> >         pad0: Sink
> >                 <- "Extension 8":1 [ENABLED,IMMUTABLE]
> > 
> > - entity 4: HP 5M Camera: HP 5M Camera (0 pad, 0 link)
> >             type Node subtype V4L flags 0
> >             device node name /dev/video1
> > 
> > - entity 8: Extension 8 (2 pads, 2 links, 0 routes)
> >             type V4L2 subdev subtype Unknown flags 0
> >         pad0: Sink
> >                 <- "Extension 4":1 [ENABLED,IMMUTABLE]
> >         pad1: Source
> >                 -> "HP 5M Camera: HP 5M Camera":0 [ENABLED,IMMUTABLE]
> > 
> > - entity 11: Extension 4 (2 pads, 2 links, 0 routes)
> >              type V4L2 subdev subtype Unknown flags 0
> >         pad0: Sink
> >                 <- "Processing 2":1 [ENABLED,IMMUTABLE]
> >         pad1: Source
> >                 -> "Extension 8":0 [ENABLED,IMMUTABLE]
> > 
> > - entity 14: Processing 2 (2 pads, 2 links, 0 routes)
> >              type V4L2 subdev subtype Unknown flags 0
> >         pad0: Sink
> >                 <- "Camera 1":0 [ENABLED,IMMUTABLE]
> >         pad1: Source
> >                 -> "Extension 4":0 [ENABLED,IMMUTABLE]
> > 
> > - entity 17: Camera 1 (1 pad, 1 link, 0 routes)
> >              type V4L2 subdev subtype Sensor flags 0
> >         pad0: Source
> >                 -> "Processing 2":0 [ENABLED,IMMUTABLE]
> > 
> > - entity 19: GPIO (0 pad, 0 link, 0 routes)
> >              type V4L2 subdev subtype Decoder flags 0
> >              device node name /dev/v4l-subdev0
> > 
> > Signed-off-by: Ricardo Ribalda <ribalda@...omium.org>
> > ---
> > Changes in v2:
> > - Rebase on top of https://patchwork.linuxtv.org/project/linux-media/patch/20241106-uvc-crashrmmod-v6-1-fbf9781c6e83@chromium.org/
> > - Create uvc_gpio_cleanup and uvc_gpio_deinit
> > - Refactor quirk: do not disable irq
> > - Change define number for MEDIA_ENT_F_GPIO
> > - Link to v1: https://lore.kernel.org/r/20241031-uvc-subdev-v1-0-a68331cedd72@chromium.org
> > 
> > ---
> > Ricardo Ribalda (5):
> >       media: uvcvideo: Factor out gpio functions to its own file
> >       Revert "media: uvcvideo: Allow entity-defined get_info and get_cur"
> >       media: uvcvideo: Create ancillary link for GPIO subdevice
> >       media: v4l2-core: Add new MEDIA_ENT_F_GPIO
> >       media: uvcvideo: Use MEDIA_ENT_F_GPIO for the GPIO entity
> > 
> > Yunke Cao (1):
> >       media: uvcvideo: Re-implement privacy GPIO as a separate subdevice
> > 
> >  .../userspace-api/media/mediactl/media-types.rst   |   4 +
> >  drivers/media/usb/uvc/Makefile                     |   3 +-
> >  drivers/media/usb/uvc/uvc_ctrl.c                   |  40 +----
> >  drivers/media/usb/uvc/uvc_driver.c                 | 123 +-------------
> >  drivers/media/usb/uvc/uvc_entity.c                 |  20 ++-
> >  drivers/media/usb/uvc/uvc_gpio.c                   | 187 +++++++++++++++++++++
> >  drivers/media/usb/uvc/uvc_video.c                  |   4 +
> >  drivers/media/usb/uvc/uvcvideo.h                   |  34 ++--
> >  drivers/media/v4l2-core/v4l2-async.c               |   3 +-
> >  include/uapi/linux/media.h                         |   1 +
> >  10 files changed, 252 insertions(+), 167 deletions(-)
> > ---
> > base-commit: 4353256f5487e0c5c47e8ff764bf4f9e679fb525
> > change-id: 20241030-uvc-subdev-89f4467a00b5

-- 
Regards,

Laurent Pinchart

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