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

[Tony Lindgren <tony-4v6yS6AI5VpBDgjK7y7TUQ@public.gmane.org>]

* Bin Liu <b-liu-l0cyMroinI0@public.gmane.org> [170120 09:24]:
> 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.

OK fine with me.

Tony
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