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

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

On Tue, Jun 18, 2019 at 06:08:50AM +0000, Robin Gong wrote:
> On 2019-06-17 at 12:15 +0200, m.olbrich@pengutronix.de wrote:
> > 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.c
> > > > > om>
> > > > > 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.
> Okay, but that's harmless, moreover, I like your comment '/* channel 0
> is special and not handled here, see run_channel0() */' which said
> clearly channel0 interrupt is a special one and NOT handled in
> sdma_int_handler. So I'd like to keep it...  

That's fine with me. I don't have a strong opinion here. It just felt wrong
to me to silently clear an interrupt that shouldn't occur in the first
place.

Michael

-- 
Pengutronix e.K.                           |                             |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |
Peiner Str. 6-8, 31137 Hildesheim, Germany | Phone: +49-5121-206917-0    |
Amtsgericht Hildesheim, HRA 2686           | Fax:   +49-5121-206917-5555 |

_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel