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

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Message-ID: <20250908115732.04e84058.michal.pecio@gmail.com>
Date: Mon, 8 Sep 2025 11:57:32 +0200
From: Michal Pecio <michal.pecio@...il.com>
To: Laurent Pinchart <laurent.pinchart@...asonboard.com>
Cc: Hans de Goede <hansg@...nel.org>, Mauro Carvalho Chehab
 <mchehab@...nel.org>, linux-media@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH] media: uvcvideo: Shorten the transfer size non
 compliance message

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@...il.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