Re: [PATCH v1] dmaengine: imx-sdma: remove BD_INTR for channel0

["m.olbrich@pengutronix.de" <m.olbrich@pengutronix.de>]

On Mon, Jun 17, 2019 at 02:14:34AM +0000, Robin Gong wrote:
> On 2019-06-14 at 18:09 +0000, Michael Olbrich wrote:
> > On Fri, Jun 14, 2019 at 09:25:51AM -0400, Sven Van Asbroeck wrote:
> > > 
> > > On Fri, Jun 14, 2019 at 6:49 AM Fabio Estevam <festevam@gmail.com>
> > > wrote:
> > > > 
> > > > 
> > > > According to the original report from Sven the issue started to
> > > > happen
> > > > on 5.0, so it would be good to add a Fixes tag and Cc stable so
> > > > that
> > > > this fix could be backported to 5.0/5.1 stable trees.
> > > Good catch !
> > > 
> > > However, the issue is highly timing-dependent. It will come and go
> > > depending
> > > on the kernel version, devicetree and defconfig. If it works for me
> > > on
> > > 4.19, that
> > > doesn't mean the bug is gone on 4.19.
> > > 
> > > Looking at the commit history, I think the commit below possibly
> > > introduced the
> > > issue. Until this commit, sdma_run_channel() would wait on the
> > > interrupt
> > > before proceeding. It has been there since 4.8:
> > > 
> > > Fixes: 1d069bfa3c78 ("dmaengine: imx-sdma: ack channel 0 IRQ in the
> > > interrupt handler")
> > I think this is correct. Starting with this commit, the interrupt
> > status fr
> > channel 0 is no longer cleared in sdma_run_channel0() and
> > sdma_int_handler() is always called for channel 0.
> > During firmware loading the interrupts are enabled again just before
> > the
> > clocks are disabled. The interrupt is pending at this moment so on a
> > single
> > core system I think this will always work as expected. If the
> > firmware
> > loading and the interrupt handler run on different cores then this is
> > racy.
> > Maybe something else changed to make this more likely?
> > 
> > With this new change sdma_int_handler() is no longer called for
> > channel 0
> > right, so you should also remove the special handling there.
> What's 'special handling' should be removed here? Do you mean put below
> pieces of your patch back?
>  static int sdma_load_script(struct sdma_engine *sdma, void *buf, int
> size,
> @@ -727,9 +720,9 @@ static irqreturn_t sdma_int_handler(int irq, void
> *dev_id)
>         unsigned long stat;
>  
>         stat = readl_relaxed(sdma->regs + SDMA_H_INTR);
> -       /* not interested in channel 0 interrupts */
> -       stat &= ~1;
>         writel_relaxed(stat, sdma->regs + SDMA_H_INTR);
> +       /* channel 0 is special and not handled here, see
> run_channel0() */
> +       stat &= ~1;

I think the "stat &= ~1;" can be removed completely. This bit should never
be set, now that the interrupt for channel 0 is disabled.

Michael

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