Message-ID: <372a4cd2-60ea-4ce8-848f-318e34d62cbf@redhat.com>
Date: Thu, 19 Dec 2024 17:05:39 +0100
From: Hans de Goede <hdegoede@...hat.com>
To: Ricardo Ribalda <ribalda@...omium.org>,
 Laurent Pinchart <laurent.pinchart@...asonboard.com>
Cc: Hans Verkuil <hverkuil@...all.nl>,
 Mauro Carvalho Chehab <mchehab@...nel.org>, linux-media@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH] media: uvcvideo: Filter hw errors while enumerating
 controls

Hi,

On 19-Dec-24 4:53 PM, Ricardo Ribalda wrote:
> On Thu, 19 Dec 2024 at 16:41, Laurent Pinchart
> <laurent.pinchart@...asonboard.com> wrote:
>>
>> On Thu, Dec 19, 2024 at 04:35:37PM +0100, Ricardo Ribalda wrote:
>>> On Thu, 19 Dec 2024 at 15:41, Laurent Pinchart wrote:
>>>> On Thu, Dec 19, 2024 at 09:17:31AM +0100, Ricardo Ribalda wrote:
>>>>> On Thu, 19 Dec 2024 at 00:27, Laurent Pinchart wrote:
>>>>>> On Fri, Dec 13, 2024 at 11:21:02AM +0000, Ricardo Ribalda wrote:
>>>>>>> To implement VIDIOC_QUERYCTRL, we need to read from the hardware all the
>>>>>>> values that were not cached previously. If that read fails, we used to
>>>>>>> report back the error to the user.
>>>>>>>
>>>>>>> Unfortunately this does not play nice with userspace. When they are
>>>>>>> enumerating the contols, the only expect an error when there are no
>>>>>>> "next" control.
>>>>>>>
>>>>>>> This is probably a corner case, and could be handled in userspace, but
>>>>>>> both v4l2-ctl and yavta fail to enumerate all the controls if we return
>>>>>>> then -EIO during VIDIOC_QUERYCTRL. I suspect that there are tons of
>>>>>>> userspace apps handling this wrongly as well.
>>>>>>>
>>>>>>> This patch get around this issue by ignoring the hardware errors and
>>>>>>> always returning 0 if a control exists.
>>>>>>>
>>>>>>> Signed-off-by: Ricardo Ribalda <ribalda@...omium.org>
>>>>>>> ---
>>>>>>> Hi 2*Hans and Laurent!
>>>>>>>
>>>>>>> I came around a device that was listing just a couple of controls when
>>>>>>> it should be listing much more.
>>>>>>>
>>>>>>> Some debugging latter I found that the device was returning -EIO when
>>>>>>> all the focal controls were read.
>>>>>>
>>>>>> Was it transient and random errors, or does the device always fail for
>>>>>> those controls ?
>>>>>
>>>>> For one of the devices the control is always failing (or I could not
>>>>> find a combination that made it work).
>>>>>
>>>>> For the other it was more or less random.
>>>>
>>>> Are there other controls that failed for that device ? And what
>>>> request(s) fail, is it only GET_CUR or also GET_MIN/GET_MAX/GET_RES ?
>>>
>>> It is a mix.
>>>
>>>> What's the approximate frequency of those random failures ?
>>>>
>>>>>>> This could be solved in userspace.. but I suspect that a lot of people
>>>>>>> has copied the implementation of v4l-utils or yavta.
>>>>>>>
>>>>>>> What do you think of this workaround?
>>>>>>
>>>>>> Pretending that the control could be queried is problematic. We'll
>>>>>> return invalid values to the user, I don't think that's a good idea. If
>>>>>> the problematic device always returns error for focus controls, we could
>>>>>> add a quirk, and extend the uvc_device_info structure to list the
>>>>>> controls to ignore.
>>>>>>
>>>>>> Another option would be to skip over controls that return -EIO within
>>>>>> the kernel, and mark those controls are broken. I think this could be
>>>>>> done transparently for userspace, the first time we try to populate the
>>>>>> cache for such controls, a -EIO error would mark the control as broken,
>>>>>> and from a userspace point of view it wouldn't be visible through as
>>>>>> ioctl.
>>>>>
>>>>> I see a couple of issues with this:
>>>>> - There are controls that fail randomly.
>>>>> - There are controls that fail based on the value of other controls
>>>>> (yeah, I know).
>>>>
>>>> I was fearing there would be random (or random-looking) failures, as
>>>> that can preclude marking the controls as broken and fully hiding them
>>>> from userspace :-(
>>>>
>>>>> - There are controls that do not implement RES, MIN, or MAX, but
>>>>> besides that, they are completely functional.
>>>>> In any of those cases we do not want to skip those controls.
>>>>>
>>>>> I am not against quirking specific cameras once we detect that they
>>>>> are broken...
>>>>
>>>> Hopefully there won't be too many of those, right ? Righhhht... ?
>>>
>>> So far I have identified 4 in a week, and I am not testing obscure
>>> camera modules....
>>
>> Can you provide more information about those modules ? USB descriptors
>> maybe, and the list of controls that fail, and how they fail ?
> 
> These are the ones I can share now:
> 
> "13d3:5519": Focus value out of range
> focus_absolute 0x009a090a (int)    : min=355 max=790 step=1 default=6
> value=500 flags=inactive

Hmm this one looks like min and default are swapped ?

So I guess this one needs a quirk which checks if default < min
and in that case swaps them (the check is to avoid swapping
with fixed fw). If these are built into chromebooks how about
doing a fwupdate for the camera instead ?

> "3277:0003": Focus returns -EIO
> Focus Absolute and Focus, Automatic Continuous: return -EIO for at
> least one of get_ max/min/res
> 
> "0408:302f": Error reading AutoExposure Flags
> UVC_GET_INFO returns invalid flags

Regards,

Hans

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