Re: 6.5.0 broke XHCI URB submissions for count >512

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

On 4.3.2024 13.57, Mathias Nyman wrote:
> On 2.3.2024 17.55, Chris Yokum wrote:
>>>> We have found a regression bug, where more than 512 URBs cannot be
>>>> reliably submitted to XHCI. URBs beyond that return 0x00 instead of
>>>> valid data in the buffer.
>>>
>>> FWIW, that's f5af638f0609af ("xhci: Fix transfer ring expansion size
>>> calculation") [v6.5-rc1] from Mathias.
>>>
> 
> Ok, I see, this could be the empty ring exception check in xhci-ring.c:
> 
> It could falsely assume ring is empty when it in fact is filled up in one
> go by queuing several small urbs.

Does this help?

diff --git a/drivers/usb/host/xhci-ring.c b/drivers/usb/host/xhci-ring.c
index 6a29ebd6682d..52278afea94b 100644
--- a/drivers/usb/host/xhci-ring.c
+++ b/drivers/usb/host/xhci-ring.c
@@ -332,7 +332,13 @@ static unsigned int xhci_ring_expansion_needed(struct xhci_hcd *xhci, struct xhc
         /* how many trbs will be queued past the enqueue segment? */
         trbs_past_seg = enq_used + num_trbs - (TRBS_PER_SEGMENT - 1);
  
-       if (trbs_past_seg <= 0)
+       /*
+        * Consider expanding the ring already if num_trbs fills the current
+        * segment (i.e. trbs_past_seg == 0), not only when num_trbs goes into
+        * the next segment. Avoids confusing full ring with special empty ring
+        * case below
+        */
+       if (trbs_past_seg < 0)
                 return 0;

Thanks
Mathias