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| author | Lukas Wunner <lukas@wunner.de> | 2019-09-11 12:15:30 +0200 |
|---|---|---|
| committer | Mark Brown <broonie@kernel.org> | 2019-09-11 15:53:11 +0100 |
| commit | 229e6af102e407feada76d3c270395d7cda2cdfe (patch) | |
| tree | 69c337a8ce180e90f95de3b08f6b351cf908223b /drivers | |
| parent | 6f6869dc97e8657e15d728c9a1ee3af2b9343990 (diff) | |
| download | linux-229e6af102e407feada76d3c270395d7cda2cdfe.tar.bz2 | |
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')
| -rw-r--r-- | drivers/spi/spi.c | 11 |
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; } |