linux-kernel - Re: [PATCH] mfd: cpcap: Fix interrupt regression with regmap clear

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Date:   Fri, 13 Nov 2020 14:06:29 -0800
From:   Tim Harvey <tharvey@...eworks.com>
To:     Lee Jones <lee.jones@...aro.org>
Cc:     Tony Lindgren <tony@...mide.com>,
        open list <linux-kernel@...r.kernel.org>,
        Carl Philipp Klemm <philipp@...s.xyz>,
        Laxminath Kasam <lkasam@...eaurora.org>,
        Merlijn Wajer <merlijn@...zup.org>,
        Mark Brown <broonie@...nel.org>, Pavel Machek <pavel@....cz>,
        Sebastian Reichel <sre@...nel.org>
Subject: Re: [PATCH] mfd: cpcap: Fix interrupt regression with regmap clear_ack

On Fri, Nov 13, 2020 at 2:21 AM Lee Jones <lee.jones@...aro.org> wrote:
>
> On Wed, 11 Nov 2020, Tony Lindgren wrote:
>
> > With commit 3a6f0fb7b8eb ("regmap: irq: Add support to clear ack
> > registers"), the cpcap interrupts are no longer getting acked properly
> > leading to a very unresponsive device with CPUs fully loaded spinning
> > in the threaded IRQ handlers.
> >
> > To me it looks like the clear_ack commit above actually fixed a long
> > standing bug in regmap_irq_thread() where we unconditionally acked the
> > interrupts earlier without considering ack_invert. And the issue with
> > cpcap started happening as we now also consider ack_invert.
> >
> > Tim Harvey <tharvey@...eworks.com> tried to fix this issue earlier with
> > "[PATCH v2] regmap: irq: fix ack-invert", but the reading of the ack
> > register was considered unnecessary for just ack_invert, and we did not
> > have clear_ack available yet. As the cpcap irqs worked both with and
> > without ack_invert earlier because of the unconditional ack, the
> > problem remained hidden until now.
> >
> > Also, looks like the earlier v3.0.8 based Motorola Android Linux kernel
> > does clear_ack style read-clear-write with "ireg_val & ~mreg_val" instead
> > of just ack_invert style write. So let's switch cpcap to use clear_ack
> > to fix the issue.
> >
> > Fixes: 3a6f0fb7b8eb ("regmap: irq: Add support to clear ack registers")
> > Cc: Carl Philipp Klemm <philipp@...s.xyz>
> > Cc: Laxminath Kasam <lkasam@...eaurora.org>
> > Cc: Merlijn Wajer <merlijn@...zup.org>
> > Cc: Mark Brown <broonie@...nel.org>
> > Cc: Pavel Machek <pavel@....cz>
> > Cc: Sebastian Reichel <sre@...nel.org>
> > Cc: Tim Harvey <tharvey@...eworks.com>
>
> It would be nice to have you review this Tim.
>

Tony / Lee,

Thanks for keeping me in the loop on this. I still haven't properly
resolved the issue with my device/driver interrupts
(drivers/mfd/gateworks_gsc.c) which requires ack_invert (writing 0 to
clearing interrupt bits).

3a6f0fb7b8eb ("regmap: irq: Add support to clear ack registers")
appears to not only add the new clear_ack case it also attempts to
resolve the long standing ack_invert issue with this change:

- ret = regmap_write(map, reg, data->status_buf[i]);
+ if (chip->ack_invert)
+      ret = regmap_write(map, reg,
+      ~data->status_buf[i]);
+ else
+     ret = regmap_write(map, reg,
+     data->status_buf[i]);

However, this still doesn't resolve the issue I have with my
device/driver because it ends up writing 1's to all the other bits in
the ack register which keeps my device's interrupt from de-asserting.
Perhaps that's a strange behavior of my device that it allows you to
'set' interrupt source bits which causes the interrupt to stay
asserted? I'm also wondering if my issue is that I currently have the
interrupt registered as such:

ret = devm_regmap_add_irq_chip(dev, gsc->regmap, client->irq,
IRQF_ONESHOT | IRQF_SHARED | IRQF_TRIGGER_FALLING, 0, &gsc_irq_chip,
&irq_data);

Perhaps this should be IRQF_TRIGGER_LOW as the device will not
de-assert its IRQ# until all source bits are cleared.

Tony, I thought that your pcap issue was that it truly did not have an
inverted ack and the fact that ack_invert did not work was why you
never noticed any issue. If this is true I would think you would want
to disable ack_invert but not necessarily enable clear_ack. Did your
testing show it needed to toggle the ack to clear it?

Best Regards,

Tim