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

[Mathias Nyman <mathias.nyman@linux.intel.com>]

On 27.1.2025 14.06, Raju Rangoju wrote:
> During the High-Speed Isochronous Audio transfers, xHCI
> controller on certain AMD platforms experiences momentary data
> loss. This results in Missed Service Errors (MSE) being
> generated by the xHCI.
> 
> The root cause of the MSE is attributed to the ISOC OUT endpoint
> being omitted from scheduling. This can happen either when an IN
> endpoint with a 64ms service interval is pre-scheduled prior to
> the ISOC OUT endpoint or when the interval of the ISOC OUT
> endpoint is shorter than that of the IN endpoint. Consequently,
> the OUT service is neglected when an IN endpoint with a service
> interval exceeding 32ms is scheduled concurrently (every 64ms in
> this scenario).
> 
> This issue is particularly seen on certain older AMD platforms.
> To mitigate this problem, it is recommended to adjust the service
> interval of the IN endpoint to not exceed 32ms (interval 8). This
> adjustment ensures that the OUT endpoint will not be bypassed,
> even if a smaller interval value is utilized.
> 
> Cc: stable@vger.kernel.org
> Signed-off-by: Raju Rangoju <Raju.Rangoju@amd.com>
> ---
> Changes since v3:
>   - Bump up the enum number XHCI_LIMIT_ENDPOINT_INTERVAL_9
> 
> Changes since v2:
>   - added stable tag to backport to all stable kernels
> 
> Changes since v1:
>   - replaced hex values with pci device names
>   - corrected the commit message
> 
>   drivers/usb/host/xhci-mem.c |  5 +++++
>   drivers/usb/host/xhci-pci.c | 25 +++++++++++++++++++++++++
>   drivers/usb/host/xhci.h     |  1 +
>   3 files changed, 31 insertions(+)
> 
> diff --git a/drivers/usb/host/xhci-mem.c b/drivers/usb/host/xhci-mem.c
> index 92703efda1f7..d3182ba98788 100644
> --- a/drivers/usb/host/xhci-mem.c
> +++ b/drivers/usb/host/xhci-mem.c
> @@ -1420,6 +1420,11 @@ int xhci_endpoint_init(struct xhci_hcd *xhci,
>   	/* Periodic endpoint bInterval limit quirk */
>   	if (usb_endpoint_xfer_int(&ep->desc) ||
>   	    usb_endpoint_xfer_isoc(&ep->desc)) {
> +		if ((xhci->quirks & XHCI_LIMIT_ENDPOINT_INTERVAL_9) &&
> +		    usb_endpoint_xfer_int(&ep->desc) &&
> +		    interval >= 9) {
> +			interval = 8;

Commit message describes this as an issue triggered by High-Speed Isoc In
endpoints that have interval larger than 32ms.

This code limits interval to 32ms for Interrupt endpoints (any speed),
should it be isoc instead?

Are Full-/Low-speed devices really also affected?

Thanks
Mathias