linux-kernel - Re: [PATCH v2] usb:gadget:uvc Do not use worker thread to pump usb requests

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Message-ID: <2023102739-reproach-salute-0d22@gregkh>
Date:   Fri, 27 Oct 2023 09:19:54 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Jayant Chowdhary <jchowdhary@...gle.com>
Cc:     mgr@...gutronix.de, Thinh.Nguyen@...opsys.com, arakesh@...gle.com,
        etalvala@...gle.com, dan.scally@...asonboard.com,
        laurent.pinchart@...asonboard.com, linux-kernel@...r.kernel.org,
        linux-usb@...r.kernel.org,
        Michael Grzeschik <m.grzeschik@...gutronix.de>
Subject: Re: [PATCH v2] usb:gadget:uvc Do not use worker thread to pump usb
 requests

On Thu, Oct 26, 2023 at 09:56:35PM +0000, Jayant Chowdhary wrote:
> This patch is based on top of
> https://lore.kernel.org/linux-usb/20230930184821.310143-1-arakesh@google.com/T/#t:

That doesn't work in the changelog of a patch at all, it goes below the
--- line p lease.

> 
> When we use an async work queue to perform the function of pumping
> usb requests to the usb controller, it is possible that thread scheduling
> affects at what cadence we're able to pump requests. This could mean usb
> requests miss their uframes - resulting in video stream flickers on the host
> device.
> 
> In this patch, we move the pumping of usb requests to
> 1) uvcg_video_complete() complete handler for both isoc + bulk
>    endpoints. We still send 0 length requests when there is no uvc buffer
>    available to encode.
> 2) uvc_v4l2_qbuf - only for bulk endpoints since it is not legal to send
>    0 length requests.
> 
> Signed-off-by: Michael Grzeschik <m.grzeschik@...gutronix.de>
> Signed-off-by: Jayant Chowdhary <jchowdhary@...gle.com>
> Suggested-by: Jayant Chowdhary <jchowdhary@...gle.com>
> Suggested-by: Avichal Rakesh <arakesh@...gle.com>
> Tested-by: Jayant Chowdhary <jchowdhary@...gle.com>
> ---
>  v1->v2: Fix code style and add self Signed-off-by

Great, but as signed-off-by kind of implies you tested it, no need for
the tested-by now, right?  Not a big deal, and normally I'd ignore it
but I know you at least have to do one more version of this based on the
above problem...

thanks,

greg k-h