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 15:56:01 +0300
From:   Vladimir Oltean <olteanv@...il.com>
To:     Mark Brown <broonie@...nel.org>
Cc:     Marc Kleine-Budde <mkl@...gutronix.de>,
        Krzysztof Kozlowski <krzk@...nel.org>,
        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 15:35, Mark Brown <broonie@...nel.org> wrote:
>

>
> Indeed.  The upshot of all this is that the interrupt needs to be freed
> not disabled before the clocks are disabled, or some other mechanism
> needs to be used to ensure that the interrupt handler won't attempt to
> access the hardware when it shouldn't.  As Vladimir says there are
> serious issues using devm for interrupt handlers (or anything else that
> might cause code to be run) due to problems like this.

And the down-shot is that whatever is done in dspi_remove (free_irq)
also needs to be done in dspi_suspend, but with extra care in
dspi_resume not only to request the irq again, but also to flush the
module's FIFOs and clear interrupts, because there might have been
nasty stuff uncaught during sleep:

    regmap_update_bits(dspi->regmap, SPI_MCR,
               SPI_MCR_CLR_TXF | SPI_MCR_CLR_RXF,
               SPI_MCR_CLR_TXF | SPI_MCR_CLR_RXF);
    regmap_write(dspi->regmap, SPI_SR, SPI_SR_CLEAR);

So it's pretty messy.

-Vladimir