spi: Guarantee cacheline alignment of driver-private data (229e6af1) · Commits · 戴 / test

__spi_alloc_controller() uses a single allocation to accommodate struct spi_controller and the driver-private data, but places the latter behind the former. This order does not guarantee cacheline alignment of the driver-private data. (It does guarantee cacheline alignment of struct spi_controller but the structure doesn't make any use of that property.) Round up struct spi_controller to cacheline size. A forthcoming commit leverages this to grant DMA access to driver-private data of the BCM2835 SPI master. An alternative, less economical approach would be to use two allocations. A third approach consists of reversing the order to conserve memory. But Mark Brown is concerned that it may result in a performance penalty on architectures that don't like unaligned accesses. Signed-off-by:

Lukas Wunner <lukas@wunner.de> Link: https://lore.kernel.org/r/01625b9b26b93417fb09d2c15ad02dfe9cdbbbe5.1568187525.git.lukas@wunner.de Signed-off-by:

Mark Brown <broonie@kernel.org>

drivers/spi/spi.c

+7 −4

Original line number	Diff line number	Diff line
		@@ -2188,8 +2188,10 @@ extern struct class spi_slave_class; /* dummy */
		* __spi_alloc_controller - allocate an SPI master or slave controller
		* @dev: the controller, possibly using the platform_bus
		* @size: how much zeroed driver-private data to allocate; the pointer to this
		* memory is in the driver_data field of the returned device,
		* accessible with spi_controller_get_devdata().
		* memory is in the driver_data field of the returned device, accessible
		* with spi_controller_get_devdata(); the memory is cacheline aligned;
		* drivers granting DMA access to portions of their private data need to
		* round up @size using ALIGN(size, dma_get_cache_alignment()).
		* @slave: flag indicating whether to allocate an SPI master (false) or SPI
		* slave (true) controller
		* Context: can sleep
		@@ -2211,11 +2213,12 @@ struct spi_controller __spi_alloc_controller(struct device dev,
		unsigned int size, bool slave)
		{
		struct spi_controller *ctlr;
		size_t ctlr_size = ALIGN(sizeof(*ctlr), dma_get_cache_alignment());

		if (!dev)
		return NULL;

		ctlr = kzalloc(size + sizeof(*ctlr), GFP_KERNEL);
		ctlr = kzalloc(size + ctlr_size, GFP_KERNEL);
		if (!ctlr)
		return NULL;

		@@ -2229,7 +2232,7 @@ struct spi_controller __spi_alloc_controller(struct device dev,
		ctlr->dev.class = &spi_master_class;
		ctlr->dev.parent = dev;
		pm_suspend_ignore_children(&ctlr->dev, true);
		spi_controller_set_devdata(ctlr, &ctlr[1]);
		spi_controller_set_devdata(ctlr, (void *)ctlr + ctlr_size);

		return ctlr;
		}

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