linux-kernel - Re: [RFC 1/1] usb: host: xhci-plat: add enable XHCI-AVOID-BEI quirk by dts

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Date: Tue, 11 Jun 2024 13:03:12 +0300
From: Mathias Nyman <mathias.nyman@...ux.intel.com>
To: joswang <joswang1221@...il.com>
Cc: mathias.nyman@...el.com, gregkh@...uxfoundation.org,
 linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
 joswang <joswang@...ovo.com>
Subject: Re: [RFC 1/1] usb: host: xhci-plat: add enable XHCI-AVOID-BEI quirk
 by dts

On 6.6.2024 17.08, joswang wrote:
> On Wed, Jun 5, 2024 at 6:31 PM Mathias Nyman
> <mathias.nyman@...ux.intel.com> wrote:
...
>>
>> I was thinking of turning XHCI_AVOID_BEI behavior into the new default, so no
>> quirk flag would be needed:
>>
>> Currently without the quirk flag:
>>
>> - ISOC TRBs trigger interrupt if TRB is the last in the TD
>>
>> Currently with XHCI_AVOID_BEI quirk flag:
>>
>> - ISOC TRBs trigger interrupt if TRB is the last in the TD
>> - Interrupt is additionally triggered every 32 isoc TRB (initially).
>> - if more than 128 events are processed in one interrupt then the
>>     32 is halved, and we trigger an interrupts every 16th isoc TRB, and so
>>     on, 16 -> 8...
>>
>> I would remove the quirk flag, and make all controllers interrupt
>> behave as if it was set. i.e. interrupt at least every 32 isoc TRB
> 
> Thank you for your detailed analysis.
> Excuse me, I have a question, do you mean to set "Currently with
> XHCI_AVOID_BEI quirk flag" as the default behavior?

Yes, unless it causes some issues or there are strong objections

>>
>> Is there an actual real world case where interrupting every 32nd ISOC TRB is
>> too often?
> 
> I mean that if the XHCI_AVOID_BEI quirk flag is set, an interrupt will
> be triggered every 8 TRBs, which makes the interrupts seem to be quite
> frequent.
> Thanks
> Jos
> 

It should start with interrupting every 32nd isoc TD, not 8th

#define AVOID_BEI_INTERVAL_MAX   32

ir->isoc_bei_interval = AVOID_BEI_INTERVAL_MAX;

Thanks
Mathias