linux-kernel - Re: [PATCH v2 0/3] xhci: ring queuing cleanups plus a quirk

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Message-ID: <72f3b497-ecac-4efe-8010-a77cc232ce30@linux.intel.com>
Date: Wed, 26 Feb 2025 14:39:28 +0200
From: Mathias Nyman <mathias.nyman@...ux.intel.com>
To: Michal Pecio <michal.pecio@...il.com>,
 Mathias Nyman <mathias.nyman@...el.com>,
 Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 0/3] xhci: ring queuing cleanups plus a quirk

On 25.2.2025 13.57, Michal Pecio wrote:
> I was looking at all uses of enqueue/dequeue pointers and I found two
> rather complex loops which appear to be doing really simple things.
> 
> I don't understand why they were written this way, it seems wasteful
> and I see nothing that should go wrong if they are replaced with much
> simpler code.
> 
> I rewrote them and the driver still works. I exercised Set TR Dequeue
> code by starting/stopping isoc streams, using usb-storage with crappy
> cable (transaction errors, halts) and also the smartctl -x trick that
> results in URB unlinks (both on usb-storage and uas) with some disks.
> 
> The third patch is a dedupe. BTW, that comment there about section
> 6.4.4.1 of the 0.95 spec seems to be wrong, I suspect it should say
> that the chain bit cannot be *cleared* because that's how the code
> works and what some commit messages say. But I don't have 0.95 spec.
> 
> New in v2:
> - dropped the patch for obsolete update_ring_for_set_deq_completion()
> - added a patch to enable the link chain quirk on one more HC
> - don't touch the chain bit in inc_enq_past_link() on quirky HCs
> - don't call inc_enq_past_link() unnecessarily
> 
> Michal Pecio (3):
>    usb: xhci: Apply the link chain quirk on NEC isoc endpoints
>    usb: xhci: Simplify moving HW Dequeue Pointer past cancelled TDs
>    usb: xhci: Unify duplicate inc_enq() code
> 

Thanks, adding Patch 1/3 and 3/3, skipping 2/3 for now.

-Mathias