linux-kernel - Re: [PATCH v4] usb: xhci: quirk for data loss in ISOC transfers

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Message-ID: <20250327103443.682f4cd1@foxbook>
Date: Thu, 27 Mar 2025 10:34:43 +0100
From: Michał Pecio <michal.pecio@...il.com>
To: "Rangoju, Raju" <raju.rangoju@....com>
Cc: gregkh@...uxfoundation.org, linux-kernel@...r.kernel.org,
 linux-usb@...r.kernel.org, mathias.nyman@...el.com,
 mathias.nyman@...ux.intel.com, stable@...r.kernel.org
Subject: Re: [PATCH v4] usb: xhci: quirk for data loss in ISOC transfers

On Thu, 27 Mar 2025 12:08:53 +0530, Rangoju, Raju wrote:
> > What if there is an ISOC IN endpoint with 64ms ESIT? I haven't yet
> > seen such a slow isoc endpoint, but I think they are allowed by the
> > spec. Your changelog suggests any periodic IN endpoint can trigger
> > this bug. 
> 
> If such an endpoint is implemented, it could theoretically contribute
> to scheduling conflicts similar to those caused by INT endpoints in
> this context. However, our observations and testing on affected
> platforms primarily involved periodic IN endpoints with service
> intervals greater than 32ms interfering with ISOC OUT endpoints.

In such case it would make sense to drop the check for
usb_endpoint_xfer_int(&ep->desc)
and rely on existing (xfer_int || xfer_isoc) in the outer 'if'.

> I'm not completely sure about this corner case if HS OUT endpoints
> can inadvertently get affected when co-existing with long-interval
> LS/FS IN endpoints. Our IP vendor confirmed that LS/FS devices are
> not affected.

There is also a third case of a FS device behind an external HS hub.
The device will look like FS to this code here, but the xHC will need
to schedule HS transactions to service it.

Regards,
Michal