From: Mark Brown <broonie@kernel.org>
To: Serge Semin <Sergey.Semin@baikalelectronics.ru>
Cc: Serge Semin <fancer.lancer@gmail.com>,
Alexey Malahov <Alexey.Malahov@baikalelectronics.ru>,
Ramil Zaripov <Ramil.Zaripov@baikalelectronics.ru>,
Pavel Parkhomenko <Pavel.Parkhomenko@baikalelectronics.ru>,
linux-spi@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [RFC PATCH] spi: Take the SPI IO-mutex in the spi_setup() method
Date: Wed, 18 Nov 2020 13:16:04 +0000 [thread overview]
Message-ID: <20201118131604.GC4827@sirena.org.uk> (raw)
In-Reply-To: <20201117094517.5654-1-Sergey.Semin@baikalelectronics.ru>
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On Tue, Nov 17, 2020 at 12:45:17PM +0300, Serge Semin wrote:
> method being called at the same time. In particular in calling the
> spi_set_cs(false) while there is an SPI-transfer being executed. In my
> case due to the commit cited above all CSs get to be switched off by
> calling the spi_setup() for /dev/spidev0.1 while there is an concurrent
> SPI-transfer execution performed on /dev/spidev0.0. Of course a situation
> of the spi_setup() being called while there is an SPI-transfer being
> executed for two different SPI peripheral devices of the same controller
> may happen not only for the spidev driver, but for instance for MMC SPI +
> some another device, or spi_setup() being called from an SPI-peripheral
> probe method while some other device has already been probed and is being
> used by a corresponding driver...
It's documented that a driver's spi_setup() operation is supposed to
support being able to be called concurrently with other transfers, see
spi-summary.rst.
> Of course I could have provided a fix affecting the DW APB SSI driver
> only, for instance, by creating a mutual exclusive access to the set_cs
> callback and setting/clearing only the bit responsible for the
> corresponding chip-select. But after a short research I've discovered that
> the problem most likely affects a lot of the other drivers:
Yeah, problems with it are very common as the documentation has noted
since forever. IIRC there was some problem triggered by trying to force
it to be serialised but I can't remember what it was.
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next prev parent reply other threads:[~2020-11-18 13:16 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-11-17 9:45 [RFC PATCH] spi: Take the SPI IO-mutex in the spi_setup() method Serge Semin
2020-11-17 10:56 ` Andy Shevchenko
2020-11-17 11:28 ` Serge Semin
2020-11-18 13:16 ` Mark Brown [this message]
2020-11-18 16:29 ` Serge Semin
2020-11-19 18:43 ` Mark Brown
2020-11-19 19:30 ` Geert Uytterhoeven
2020-11-20 17:17 ` Mark Brown
2020-11-20 17:26 ` Serge Semin
2020-11-20 21:35 ` Mark Brown
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