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

[Robin Gong <yibin.gong@nxp.com>]

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;

> 
> Michael
>