Re: [PATCH v6 5/5] media: uvcvideo: Flush the control cache when we get an event

Hans de Goede
2024-12-09T15:24:56Z

Hi,

On 9-Dec-24 12:31 PM, Ricardo Ribalda wrote:
> Hi Hans
>
> On Mon, 9 Dec 2024 at 12:03, Hans de Goede <hdegoede@redhat.com> wrote:
>>
>> Hi Ricardo,
>>
>> On 3-Dec-24 10:20 PM, Ricardo Ribalda wrote:
>>> Asynchronous controls trigger an event when they have completed their
>>> operation.
>>>
>>> This can make that the control cached value does not match the value in
>>> the device.
>>>
>>> Let's flush the cache to be on the safe side.
>>>
>>> Signed-off-by: Ricardo Ribalda <ribalda@chromium.org>
>>
>> Thank you for your patch.
>>
>> It seems that you have missed Laurent's reply asking to improve the commit message:
>>
>> "Conceptually this change looks fine, but the commit message needs to
>> explain why this is safe to do without protecting ctrl->loaded with a
>> lock."
>>
>> https://lore.kernel.org/linux-media/20241203203748.GD5196@pendragon.ideasonboard.com/
>>
>> Or maybe the posting of this v6 and that reply have crossed each other.
>
> In this v6 I moved loaded=0 from uvc_ctrl_status_event_async() to
> uvc_ctrl_status_event()

Ah I missed that you moved it, my bad.

> Now setting loaded=0 is just after mutex_lock(&chain->ctrl_mutex);
>
> Do we need a new version?

Since the setting is now clearly done under the lock the new version seems
good to me as is.

So I have now merged this into:

https://gitlab.freedesktop.org/linux-media/users/uvc/-/commits/next/

Regards,

Hans

>
>>
>> Either way please post a new version addressing this comment.
>>
>> Thanks & Regards,
>>
>> Hans
>>
>>
>>
>>> ---
>>> drivers/media/usb/uvc/uvc_ctrl.c | 3 +++
>>> 1 file changed, 3 insertions(+)
>>>
>>> diff --git a/drivers/media/usb/uvc/uvc_ctrl.c b/drivers/media/usb/uvc/uvc_ctrl.c
>>> index 3dc9b7a49f64..db29e0e8bfd4 100644
>>> --- a/drivers/media/usb/uvc/uvc_ctrl.c
>>> +++ b/drivers/media/usb/uvc/uvc_ctrl.c
>>> @@ -1622,6 +1622,9 @@ void uvc_ctrl_status_event(struct uvc_video_chain *chain,
>>>
>>> mutex_lock(&chain->ctrl_mutex);
>>>
>>> + /* Flush the control cache, the data might have changed. */
>>> + ctrl->loaded = 0;
>>> +
>>> handle = ctrl->handle;
>>> if (handle)
>>> uvc_ctrl_set_handle(handle, ctrl, NULL);
>>>
>>
>
>