spi: Take the SPI IO-mutex in the spi_setup() method
I've discovered that due to the recent commit49d7d695ca
("spi: dw: Explicitly de-assert CS on SPI transfer completion") a concurrent usage of the spidev devices with different chip-selects causes the "SPI transfer timed out" error. The root cause of the problem has turned to be in a race condition of the SPI-transfer execution procedure and the spi_setup() 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... 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: - drivers/spi/spi-sun4i.c - RMW the chip-select register; - drivers/spi/spi-rockchip.c - RMW the chip-select register; - drivers/spi/spi-qup.c - RMW a generic force-CS flag in a CSR. - drivers/spi/spi-sifive.c - set a generic CS-mode flag in a CSR. - drivers/spi/spi-bcm63xx-hsspi.c - uses an internal mutex to serialize the bus config changes, but still isn't protected from the race condition described above; - drivers/spi/spi-geni-qcom.c - RMW a chip-select internal flag and set the CS state in HW; - drivers/spi/spi-orion.c - RMW a chip-select register; - drivers/spi/spi-cadence.c - RMW a chip-select register; - drivers/spi/spi-armada-3700.c - RMW a chip-select register; - drivers/spi/spi-lantiq-ssc.c - overwrites the chip-select register; - drivers/spi/spi-sun6i.c - RMW a chip-select register; - drivers/spi/spi-synquacer.c - RMW a chip-select register; - drivers/spi/spi-altera.c - directly sets the chip-select state; - drivers/spi/spi-omap2-mcspi.c - RMW an internally cached CS state and writes it to HW; - drivers/spi/spi-mt65xx.c - RMW some CSR; - drivers/spi/spi-jcore.c - directly sets the chip-selects state; - drivers/spi/spi-mt7621.c - RMW a chip-select register; I could have missed some drivers, but a scale of the problem is obvious. As you can see most of the drivers perform an unprotected Read-modify-write chip-select register modification in the set_cs callback. Seeing the spi_setup() function is calling the spi_set_cs() and it can be executed concurrently with SPI-transfers exec procedure, which also calls spi_set_cs() in the SPI core spi_transfer_one_message() method, the race condition of the register modification turns to be obvious. To sum up the problem denoted above affects each driver for a controller having more than one chip-select lane and which: 1) performs the RMW to some CS-related register with no serialization; 2) directly disables any CS on spi_set_cs(dev, false). * the later is the case of the DW APB SSI driver. The controllers which equipped with a single CS theoretically can also experience the problem, but in practice will not since normally the spi_setup() isn't called concurrently with the SPI-transfers executed on the same SPI peripheral device. In order to generically fix the denoted bug I'd suggest to serialize an access to the controller IO by taking the IO mutex in the spi_setup() callback. The mutex is held while there is an SPI communication going on on the SPI-bus of the corresponding SPI-controller. So calling the spi_setup() method and disabling/updating the CS state within it would be safe while there is no any SPI-transfers being executed. Also note I suppose it would be safer to protect the spi_controller->setup() callback invocation too, seeing some of the SPI-controller drivers update a HW state in there. Fixes:49d7d695ca
("spi: dw: Explicitly de-assert CS on SPI transfer completion") Signed-off-by: Serge Semin <Sergey.Semin@baikalelectronics.ru> Link: https://lore.kernel.org/r/20201117094517.5654-1-Sergey.Semin@baikalelectronics.ru Signed-off-by: Mark Brown <broonie@kernel.org>
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@ -3372,12 +3372,15 @@ int spi_setup(struct spi_device *spi)
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if (!spi->max_speed_hz)
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spi->max_speed_hz = spi->controller->max_speed_hz;
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mutex_lock(&spi->controller->io_mutex);
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if (spi->controller->setup)
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status = spi->controller->setup(spi);
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if (spi->controller->auto_runtime_pm && spi->controller->set_cs) {
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status = pm_runtime_get_sync(spi->controller->dev.parent);
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if (status < 0) {
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mutex_unlock(&spi->controller->io_mutex);
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pm_runtime_put_noidle(spi->controller->dev.parent);
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dev_err(&spi->controller->dev, "Failed to power device: %d\n",
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status);
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@ -3399,6 +3402,8 @@ int spi_setup(struct spi_device *spi)
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spi_set_cs(spi, false);
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}
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mutex_unlock(&spi->controller->io_mutex);
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if (spi->rt && !spi->controller->rt) {
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spi->controller->rt = true;
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spi_set_thread_rt(spi->controller);
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