Re: [PATCH v3 4/5] usb: musb: musb_cppi41: Workaround DMA stall issue during teardown

[Bin Liu <b-liu-l0cyMroinI0@public.gmane.org>]

On Thu, Jan 19, 2017 at 08:56:46AM -0800, Tony Lindgren wrote:
> * Alexandre Bailon <abailon-rdvid1DuHRBWk0Htik3J/w@public.gmane.org> [170119 06:09]:
> > The DMA may hung up if a teardown is initiated while an endpoint is still
> > active (Advisory 2.3.27 of DA8xx errata).
> > To workaround this issue, add a delay before to initiate the teardown.
> > 
> > Signed-off-by: Alexandre Bailon <abailon-rdvid1DuHRBWk0Htik3J/w@public.gmane.org>
> > ---
> >  drivers/usb/musb/da8xx.c       | 2 +-
> >  drivers/usb/musb/musb_core.h   | 1 +
> >  drivers/usb/musb/musb_cppi41.c | 4 ++++
> >  3 files changed, 6 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/usb/musb/da8xx.c b/drivers/usb/musb/da8xx.c
> > index 5f50a78..8c9850c 100644
> > --- a/drivers/usb/musb/da8xx.c
> > +++ b/drivers/usb/musb/da8xx.c
> > @@ -483,7 +483,7 @@ da8xx_dma_controller_create(struct musb *musb, void __iomem *base)
> >  #endif
> >  
> >  static const struct musb_platform_ops da8xx_ops = {
> > -	.quirks		= MUSB_INDEXED_EP | MUSB_DMA_CPPI41,
> > +	.quirks		= MUSB_INDEXED_EP | MUSB_DMA_CPPI41 | MUSB_DA8XX,
> >  	.init		= da8xx_musb_init,
> >  	.exit		= da8xx_musb_exit,
> >  
> > diff --git a/drivers/usb/musb/musb_core.h b/drivers/usb/musb/musb_core.h
> > index ade902e..d129278 100644
> > --- a/drivers/usb/musb/musb_core.h
> > +++ b/drivers/usb/musb/musb_core.h
> > @@ -172,6 +172,7 @@ struct musb_io;
> >   */
> >  struct musb_platform_ops {
> >  
> > +#define MUSB_DA8XX		BIT(7)
> >  #define MUSB_DMA_UX500		BIT(6)
> >  #define MUSB_DMA_CPPI41		BIT(5)
> >  #define MUSB_DMA_CPPI		BIT(4)
> > diff --git a/drivers/usb/musb/musb_cppi41.c b/drivers/usb/musb/musb_cppi41.c
> > index 1fe7eae..d371d05 100644
> > --- a/drivers/usb/musb/musb_cppi41.c
> > +++ b/drivers/usb/musb/musb_cppi41.c
> > @@ -554,6 +554,10 @@ static int cppi41_dma_channel_abort(struct dma_channel *channel)
> >  		}
> >  	}
> >  
> > +	/* DA8xx Advisory 2.3.27: wait 250 ms before to start the teardown */
> > +	if (musb->io.quirks & MUSB_DA8XX)
> > +		mdelay(250);
> > +
> >  	tdbit = 1 << cppi41_channel->port_num;
> >  	if (is_tx)
> >  		tdbit <<= 16;
> 
> How about replace the do while loop calling  dmaengine_terminate_all() with
> deferred work doing that?

It would be great, but it seems a little hard to implement. If the
_abort is initiated by application due to transfer timeout, the
application might immediately retry the transfer, then the driver would
have to ensure the deferred work is done and the channel is free by that
time.

I guess we have to evaluate the impact of the do-while loop and the
performance impact of the deferred work to know if it is worth it.

> 
> That way it's more generic as it seems there's no hurry doing that
> after the musb registers are cleared. That would also allow getting rid of
> the two current udelay() calls there that also seems nasty.

I don't think replacing the do-while loop will allow to get rid of the
two udelay() calls, which are there as barriers for the register changes
- clearing MUSB_RXCSR_DMAENAB and flushing FIFO.

Regards,
-Bin.
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