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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>
This commit is contained in:
Lukas Wunner 2019-09-11 12:15:30 +02:00 committed by Mark Brown
parent 6f6869dc97
commit 229e6af102
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GPG Key ID: 24D68B725D5487D0
1 changed files with 7 additions and 4 deletions
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11
drivers/spi/spi.c
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@ -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;
}