linux-kernel - Re: [PATCH] gpiolib: Don't implicitly disable irq when masking

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Message-ID: <CACRpkdb1UFQ=1gePeBBEQ3ODu+6m0dHBqaxdtOF9Qc01WytMEQ@mail.gmail.com>
Date:   Thu, 11 May 2023 10:00:57 +0200
From:   Linus Walleij <linus.walleij@...aro.org>
To:     Chris Packham <Chris.Packham@...iedtelesis.co.nz>
Cc:     "andy.shevchenko@...il.com" <andy.shevchenko@...il.com>,
        "brgl@...ev.pl" <brgl@...ev.pl>,
        Ben Brown <Ben.Brown@...iedtelesis.co.nz>,
        "linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Marc Zyngier <maz@...nel.org>,
        Hans Verkuil <hverkuil-cisco@...all.nl>
Subject: Re: [PATCH] gpiolib: Don't implicitly disable irq when masking

On Wed, May 10, 2023 at 10:59 PM Chris Packham
<Chris.Packham@...iedtelesis.co.nz> wrote:

> The coupling of gpiochip_irq_mask()/gpiochip_irq_unmask() with
> gpiochip_disable_irq()/gpiochip_enable_irq() goes back to the same
> commit a8173820f441 ("gpio: gpiolib: Allow GPIO IRQs to lazy disable").
> It's not immediately obvious to me why the coupling is needed.

That is just a refactoring of what existed before.

The use case is here:
drivers/media/cec/platform/cec-gpio/cec-gpio.c

The driver needs to switch, at runtime, between actively driving a GPIO
line with gpiod_set_value(), and setting the same line into input mode
and listening for signalling triggering IRQs on it, and then back to
output mode and driving the line again. It's a bidirectional GPIO line.
This use case yields a high need of control.

> I was
> hoping that someone seeing my patch would confirm that it's not needed
> or say why it's needed suggest an alternative approach.

Which IRQ-enabled gpiochip is this? Has it been converted to be immutable?
I think that could be part of the problem.

Yours,
Linus Walleij