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

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Message-ID: <9265b40f-b803-4dd7-b6df-3e8cb510b07b@rowland.harvard.edu>
Date: Tue, 5 Nov 2024 09:13:41 -0500
From: Alan Stern <stern@...land.harvard.edu>
To: Raju Rangoju <Raju.Rangoju@....com>
Cc: linux-usb@...r.kernel.org, mathias.nyman@...el.com,
	gregkh@...uxfoundation.org, linux-kernel@...r.kernel.org,
	stable@...r.kernel.org
Subject: Re: [PATCH] usb: xhci: quirk for data loss in ISOC transfers

On Tue, Nov 05, 2024 at 02:48:50PM +0530, 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 exceed 32ms (interval 8). This

Do you mean "not to exceed 32 ms"?

> adjustment ensures that the OUT endpoint will not be bypassed,
> even if a smaller interval value is utilized.
> 
> Cc: stable@...r.kernel.org
> Signed-off-by: Raju Rangoju <Raju.Rangoju@....com>
> ---
>  drivers/usb/host/xhci-mem.c |  5 +++++
>  drivers/usb/host/xhci-pci.c | 14 ++++++++++++++
>  drivers/usb/host/xhci.h     |  1 +
>  3 files changed, 20 insertions(+)
> 
> diff --git a/drivers/usb/host/xhci-mem.c b/drivers/usb/host/xhci-mem.c
> index d2900197a49e..4892bb9afa6e 100644
> --- a/drivers/usb/host/xhci-mem.c
> +++ b/drivers/usb/host/xhci-mem.c
> @@ -1426,6 +1426,11 @@ 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;
> +		}

This change ensures that the interval is <= 32 ms.

Alan Stern