Warning dump on OMAP-L138 when g_zero module is removed

[Alexandre Bailon]

Hi Sekhar,
On 07/21/2017 05:18 PM, Alexandre Bailon wrote:
> Hi Sekhar,
>
> On 07/10/2017 01:00 PM, Sekhar Nori wrote:
> > On Thursday 06 July 2017 10:43 PM, Alexandre Bailon wrote:
> >> On 06/29/2017 03:50 PM, Sekhar Nori wrote:
> >>> Hi Alexandre, Bin,
> >>>
> >>> With latest linux-next, I see a warning dump when I remove g_zero[1] on
> >>> OMAP-L138 LCDK board. I am building the kernel with davinci_all_defconfig.
> >>>
> >>> It is not present in latest mainline because the warnings are introduced
> >>> with CPPI DMA getting enabled in latest -next.
> >>>
> >>> Subsequent insertion of g_ether leads to a warning too[2], although the
> >>> gadget seems to work (ping test).
> >>>
> >>> Since these are pretty annoying, it will be nice to get rid of them. I
> >>> have not been able to debug any further. But if you have
> >>> ideas/experiments to try, I can do that.
> >
> >> I got a lot of these warnings during development but it was only for the
> >> host mode.
> >> If I remember correctly, the cause was a race between the teardown
> >> function and the interrupt handler.
> >> The teardwon descriptor was pop from the queue by the interrupt handler,
> >> preventing cppi41_tear_down_chan() to get it, which will result after
> >> some retries to a couple of warnings.
> >>
> >> I will take a look to see if that is the same issue.
> That is not the same issue. Still, for some reasons, we never get the
> teardown descriptor.
> Two possibilities:
>  - Like the issue I had, the teardown is pop at the wrong place.
>  - The teardown doesn't complete or the descriptor is not queued.
The teardown descriptor is not queued. I have figured out the reason.
The function cppi41_dma_channel_abort() enable the teardown by setting the bit corresponding to the endpoint number.
The address of the register is USB_TDOWN but actually the address is wrong in the case of DA8xx.
Using the right address (0x1c) fix the teardown warnings.
I will work on a fix.
> I think we should eliminate the first one before to work on the second one.
> I think adding some logs to cppi41_pop_desc() could help to figure out
> what is happening.
> >
> > Thanks! I also see similar warnings under fast ping traffic and g_ether
> > inserted on LCDK. They dont come immediately though. Only after an hour
> > or so under traffic.
The fix should also fix this issue.
> I would not have expected to have them during a ping but this probably
> happens because some USB packet have timed out, which cause may a teardown.
> >
> > I can those provide logs too if its going to be helpful.
> Currently, I think we should focus on the warnings that happens during
> the rmmod as they are always reproducible.
>
> Thanks,
> Alexandre
>
Note that the teardown is not the only thing that doesn't work correctly.
I think same kind of issue should apply to the autoreq and the dma mode.
I will work on a patch that should solve all of them.

Thanks,
Alexandre