Re: [Qemu-devel] xhci: move command stop and command abort flag check to the case when the crcr_low register is set

[Jaroslav Jindrák]

Hi,

that was an error on my part, I was debugging the non-working command ring
abort/stop functionality and as
the xhci driver implementation I was working on used crcr_low and crcr_high
as two separate registers it did not
hit me it was actually my way of accessing them that caused the abort/stop
to not work.

Thank you very much for the correction and I apologise for disturbing you,
hope I didn't eat too much of your time.

Have a nice day,
Jaroslav Jindrak

S pozdravem,
Jaroslav Jindrak

On 21 August 2017 at 14:23, Gerd Hoffmann <address@hidden> wrote:

> On Tue, 2017-08-01 at 01:48 +0200, Jaroslav Jindrák wrote:
> > Hello,
> >
> > I'd like to submit a patch to the xhci subsystem of QEMU. Currently,
> > when the command stop or command abort flags in the crcr_low register
> > are set, nothing happens. This is because the part of the code that
> > tests those two flags (and performs command ring abort/stop) is in
> > the crcr_high case. This error has a simple workaround - after
> > writing to the crcr_low register with either of these two flags set,
> > one can write the value of crcr_high to crcr_high, so I
> > assume this fix does not have that big of a priority, but a driver
> > that follows the specification strictly would misbehave in this kind
> > of situation (stopping/aborting the command ring).
>
> Specs says (section 5.1, Register Conventions):
>
> <quote>
> If the xHC supports 64-bit addressing (AC64 = ‘1’), then software
> should write registers containing 64-bit address fields using only
> Qword accesses. If a system is incapable of issuing Qword accesses,
> then writes to the 64-bit address fields shall be performed using 2
> Dword accesses; low Dword-first, high-Dword second.
> </quote>
>
> So I think the guest must write both crcr_low and crcr_high, and the
> qemu behavior is correct.
>
> Are there any guests which actually have problems?
>
> cheers,
>   Gerd
>
>