linux-kernel - Re: [PATCH] media: uvcvideo: Support large SuperSpeedPlus isochronous endpoints

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Message-ID: <2025042101-coyness-vitality-e636@gregkh>
Date: Mon, 21 Apr 2025 10:51:38 +0200
From: Greg KH <gregkh@...uxfoundation.org>
To: Michal Pecio <michal.pecio@...il.com>
Cc: Laurent Pinchart <laurent.pinchart@...asonboard.com>,
	Hans de Goede <hdegoede@...hat.com>,
	Mauro Carvalho Chehab <mchehab@...nel.org>,
	linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-usb@...r.kernel.org
Subject: Re: [PATCH] media: uvcvideo: Support large SuperSpeedPlus
 isochronous endpoints

On Mon, Apr 21, 2025 at 09:59:51AM +0200, Michal Pecio wrote:
> USB 3.1 increased maximum isochronous bandwidth to 96KB per interval,
> too much for 16 bits and the SuperSpeed Endpoint Companion descriptor.
> A new SuperSpeedPlus Isochronous Endpoint Companion descriptor was
> introduced to encode such bandwidths, see spec sections 9.6.7, 9.6.8.
> 
> Support the descriptor with code based on xhci_get_max_esit_payload()
> and widen all 'psize' variables to 32 bits. Subsequent calculations
> are 32 bit already and not expected to overflow, so this change ought
> to suffice for proper alt setting selection on USB 3.x Gen 2 devices.
> 
> Signed-off-by: Michal Pecio <michal.pecio@...il.com>
> ---
> 
> This change appears to be a strict necessity for supporting USB3 Gen2
> isochronous devices meaningfully. Whether it's sufficient I don't know,
> I don't have such HW. No regression seen on High Speed and SuperSpeed.

If you don't have the hardware, why make this change?

>  drivers/media/usb/uvc/uvc_

This line looks odd, because:

>  drivers/media/usb/uvc/uvc_driver.c |  2 +-
>  drivers/media/usb/uvc/uvc_video.c  | 13 +++++++++----
>  drivers/media/usb/uvc/uvcvideo.h   |  4 ++--
>  3 files changed, 12 insertions(+), 7 deletions(-)

Only 3 files were changed.  What went wrong?

thanks,

greg k-h