linux-kernel - Re: [PATCH v1] hwmon: (lm90) Use edge-triggered interrupt

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Message-ID: <20210617151236.GB2676642@roeck-us.net>
Date:   Thu, 17 Jun 2021 08:12:36 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Dmitry Osipenko <digetx@...il.com>
Cc:     Jean Delvare <jdelvare@...e.com>, linux-kernel@...r.kernel.org,
        linux-hwmon@...r.kernel.org
Subject: Re: [PATCH v1] hwmon: (lm90) Use edge-triggered interrupt

On Thu, Jun 17, 2021 at 05:46:33PM +0300, Dmitry Osipenko wrote:
> 17.06.2021 17:13, Guenter Roeck пишет:
> ...
> >> This is a device-tree based system, in particular it's NVIDIA Tegra30
> >> Nexus 7. The interrupt support was originally added to the lm90 driver
> >> by Wei Ni who works at NVIDIA and did it for the Tegra boards. The Tegra
> >> device-trees are specifying the trigger mask and apparently they all are
> >> cargo-culted and wrong because they use IRQ_TYPE_LEVEL_HIGH, while it
> > 
> > Be fair, no one is perfect.
> 
> This is a very minor problem, so no wonder that nobody noticed or
> bothered to fix it yet. I'm just clarifying the status here.
> 
> >> should be IRQ_TYPE_EDGE_FALLING.
> > 
> > It should probably be both IRQ_TYPE_EDGE_FALLING and IRQ_TYPE_EDGE_RISING,
> 
> For now I see that the rising edge isn't needed, the TEMP_ALERT goes
> HIGH by itself when temperature backs to normal. But I will try to
> double check.
> 
The point is that a sysfs event should be sent to userspace on both
edges, not only when an alarm is raised. But, you are correct,
IRQ_TYPE_EDGE_RISING is currently not needed since sysfs events
are not generated.

> > and the interrupt handler should call hwmon_notify_event() instead of
> > clogging the kernel log, but that should be done in a separate patch.
> 
> Thank you for suggestion, I will take a look.
> 
> > Anyway, the tegra30 dts files in the upstream kernel either use
> > IRQ_TYPE_LEVEL_LOW or no interrupts for nct1008. The Nexus 7 dts file
> > in the upstream kernel has no interrupt configured (and coincidentally
> > it was you who added that entry). Where do you see IRQ_TYPE_LEVEL_HIGH ?
> 
> I have a patch that will add the interrupt property, it's stashed
> locally for the next kernel release.
> 
> IIUC, it's not only the Tegra30 dts, but all the TegraXXX boards that
> use IRQ_TYPE_LEVEL_LOW are in the same position.

I still don't see a IRQ_TYPE_LEVEL_HIGH, though.

Thanks,
Guenter

> 
> >> The IRQF flag in devm_request_threaded_irq() overrides the trigger mask
> >> specified in a device-tree. IIUC, the interrupt is used only by OF-based
> >> devices, hence I think we could simply remove the IRQF flag from the
> >> code and fix the device-trees. Does it sound good to you?
> > 
> > Yes, that is a better approach.
> 
> Thank you for reviewing this patch. I'll prepare v2.