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

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Message-ID: <29815488-2ee8-b7a4-8454-45c3b37e5c14@amd.com>
Date: Thu, 7 Nov 2024 16:55:47 +0530
From: "Rangoju, Raju" <raju.rangoju@....com>
To: Alan Stern <stern@...land.harvard.edu>
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 11/5/2024 7:43 PM, Alan Stern wrote:
> 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.

That's correct, thanks for pointing it out. I'll take care of this in V2.

> 
> Alan Stern