Re: [RFC] usb: dwc2: hcd: fix split schedule issue

[Doug Anderson]

John,

On Wed, Nov 11, 2015 at 8:29 PM, John Youn <John.Youn@xxxxxxxxxxxx> wrote:
> On 11/11/2015 4:22 PM, Doug Anderson wrote:
>> John,
>>
>> On Fri, Nov 6, 2015 at 2:04 AM, Yunzhi Li <lyz@xxxxxxxxxxxxxx> wrote:
>>> hi John ,
>>>
>>>   As we talked yesterday, I tried to fix the split schedule sequence. This
>>> patch will
>>> avoid scheduling SSPLIT-IN packet for another device between
>>> SSPLIT-OUT-begin and
>>> SSPLIT-OUT-end, now the keyboard and Jebra audio speaker could work together
>>> well, but
>>> I'm not sure if this is exactly the right way to schedule split transfers
>>> and if there
>>> is any dide effect with this patch. Please help review this patch. Thanks.
>>>
>>>> Fix dwc2 split schedule sequence issue. Not schedule a SSPLIT_IN
>>>> packet between SSPLIT-begin and SSPLIT-end.
>>>>
>>>> Signed-off-by: Yunzhi Li <lyz@xxxxxxxxxxxxxx>
>>>> ---
>>>>   drivers/usb/dwc2/hcd.c | 4 ++++
>>>>   1 file changed, 4 insertions(+)
>>
>> Did you have any thoughts on this patch?  Although this patch didn't
>> fix the problems I was seeing with the Microsoft Wireless Keyboard
>> (see the patch I sent out earlier which does seem to fix it), I can
>> confirm that in a different setup (HUB goes to USB audio + mouse) that
>> this patch does fix some problems.
>>
>> That being said, it feels to me like a band-aid rather than an actual
>> fix (I'm talking out of my rear end, though, since my USB experience
>> is lacking at best).  It feels like perhaps we're just not keeping
>> track the xact_pos correctly, but of course I don't know that for
>> sure...
>>
>> Anyway, just fishing...  ;)
>>
>> -Doug
>>
>
> Hi Doug,
>
> I also feel it is not quite right as the SSPLIT should be able to
> happen during the SSPLIT of another device. I tried to reproduce
> and see the same scheduling but don't see any hang due to it.
>
> Yunzhi, any details on what kind of hub and keyboard you are
> using? I have the same Jabra 410 speaker.

Just to tie things together for anyone following along, my current
thoughts on how to fix this are something like
<https://patchwork.kernel.org/patch/7631551/>.

-Doug
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