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authorLukas Wunner <lukas@wunner.de>2019-09-11 12:15:30 +0200
committerMark Brown <broonie@kernel.org>2019-09-11 15:53:11 +0100
commit229e6af102e407feada76d3c270395d7cda2cdfe (patch)
tree69c337a8ce180e90f95de3b08f6b351cf908223b /drivers/spi
parent6f6869dc97e8657e15d728c9a1ee3af2b9343990 (diff)
spi: Guarantee cacheline alignment of driver-private data
__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>
Diffstat (limited to 'drivers/spi')
-rw-r--r--drivers/spi/spi.c11
1 files changed, 7 insertions, 4 deletions
diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c
index b2890923d256..f8b4654a57d3 100644
--- a/drivers/spi/spi.c
+++ b/drivers/spi/spi.c
@@ -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;
}