linux-kernel - Re: [PATCH v2 1/3] spi: spi-fsl-dspi: Fix external abort on interrupt in exit paths

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Date:   Mon, 15 Jun 2020 17:59:33 +0300
From:   Vladimir Oltean <olteanv@...il.com>
To:     Krzysztof Kozlowski <krzk@...nel.org>
Cc:     Mark Brown <broonie@...nel.org>,
        Marc Kleine-Budde <mkl@...gutronix.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Vladimir Oltean <vladimir.oltean@....com>,
        linux-spi <linux-spi@...r.kernel.org>,
        lkml <linux-kernel@...r.kernel.org>,
        Wolfram Sang <wsa@...nel.org>, stable@...r.kernel.org,
        Pengutronix Kernel Team <kernel@...gutronix.de>
Subject: Re: [PATCH v2 1/3] spi: spi-fsl-dspi: Fix external abort on interrupt
 in exit paths

On Mon, 15 Jun 2020 at 17:57, Krzysztof Kozlowski <krzk@...nel.org> wrote:
>
> On Mon, Jun 15, 2020 at 05:23:28PM +0300, Vladimir Oltean wrote:
> > On Mon, 15 Jun 2020 at 16:41, Krzysztof Kozlowski <krzk@...nel.org> wrote:
> > >
> > > On Mon, Jun 15, 2020 at 04:12:28PM +0300, Vladimir Oltean wrote:
> > > > On Mon, 15 Jun 2020 at 16:10, Mark Brown <broonie@...nel.org> wrote:
> > > >
> > > > >
> > > > > It's a bit unusual to need to actually free the IRQ over suspend -
> > > > > what's driving that requirement here?
> > > >
> > > > clk_disable_unprepare(dspi->clk); is driving the requirement - same as
> > > > in dspi_remove case, the module will fault when its registers are
> > > > accessed without a clock.
> > >
> > > In few cases when I have shared interrupt in different drivers, they
> > > were just disabling it during suspend. Why it has to be freed?
> > >
> > > Best regards,
> > > Krzysztof
> > >
> >
> > Not saying it _has_ to be freed, just to be prevented from running
> > concurrently with us disabling the clock.
> > But if we can get away in dspi_suspend with just disable_irq, can't we
> > also get away in dspi_remove with just devm_free_irq?
>
> One reason why they have to be different could be following scenario:
> 1. Device could be unbound any time and disabling IRQ in remove() would
>    effectively disable the IRQ also for other devices using this shared
>    line. First disable_irq() really disables it, the latter just
>    increases the counter.
> 2. However during system suspend, it is expected that all drivers in
>    their suspend (and later resume) callbacks will do the same - disable
>    the shared IRQ line. And finally the system disables interrupts
>    globally so the line will be balanced.
>
> Freeing IRQ solves the case #1 without causing any imbalance between
> enables/disables or requests/frees.  Disabling IRQ solves the #2, also
> without any imbalance.
>
> Best regards,
> Krzysztof
>
>
>

So the answer to my question is 'yes', right?