Re: [PATCH] media: uvcvideo: Shorten the transfer size non compliance message

Michal Pecio
2025-09-08T09:57:39Z

On Mon, 8 Sep 2025 10:36:55 +0200, Laurent Pinchart wrote:
> On Thu, Sep 04, 2025 at 08:14:29AM +0200, Michal Pecio wrote:
> > This message is much longer than others and doesn't fit even in a 160
> > column window when printed, despite providing little real information.
> >
> > Also replace 'transmission' with 'transfer' because that's the actual
> > name and 'max packet' with 'limit' because it isn't same thing with
> > isochronus endpoints. Remove cryptic abbreviations like 'ep'.
> >
> > Signed-off-by: Michal Pecio <michal.pecio@gmail.com>
> > ---
> >
> > By the way, this hack doesn't help much in the opposite case:
> > dwMaxPayloadTransferSize is right, but EP descriptors are a mess.
>
> Have you encountered such devices ?

Yes, it sometimes reports bad 'mult' in EP descriptors, which leaves
them with insufficient BW for some video modes. Can be fixed with the
usual "turn it off, turn it on again".

I frankly haven't bothered trying what would happen if I override mult
in USB core and I think it would be crazy to send that upstream anyway.

Before that patch, it would simply fail with "no fast enough alt
setting" and -EIO or some such seen by userspace. Now it produces
truncated frames. But also nothing worse than that, so it's fine.

Regards,
Michal