diff options
author | Russell King <rmk+kernel@arm.linux.org.uk> | 2010-09-08 16:27:56 +0100 |
---|---|---|
committer | Russell King <rmk+kernel@arm.linux.org.uk> | 2010-09-08 16:27:56 +0100 |
commit | 2be23c475af8ae4e25f8bab08d815b17593bd547 (patch) | |
tree | 864cf9dca5faaa51c9346a8835c8f101bd5c8fa2 | |
parent | a387f0f5409276c5cf75eecb61ef6e6896f851b4 (diff) |
ARM: Ensure PTE modifications via dma_alloc_coherent are visible
Dave Hylands reports:
| We've observed a problem with dma_alloc_writecombine when the system
| is under heavy load (heavy bus traffic). We've managed to reduce the
| problem to the following snippet, which is run from a kthread in a
| continuous loop:
|
| void *virtAddr;
| dma_addr_t physAddr;
| unsigned int numBytes = 256;
|
| for (;;) {
| virtAddr = dma_alloc_writecombine(NULL,
| numBytes, &physAddr, GFP_KERNEL);
| if (virtAddr == NULL) {
| printk(KERN_ERR "Running out of memory\n");
| break;
| }
|
| /* access DMA memory allocated */
| tmp = virtAddr;
| *tmp = 0x77;
|
| /* free DMA memory */
| dma_free_writecombine(NULL,
| numBytes, virtAddr, physAddr);
|
| ...sleep here...
| }
|
| By itself, the code will run forever with no issues. However, as we
| increase our bus traffic (typically using DMA) then the *tmp = 0x77
| line will eventually cause a page fault. If we add a small delay (a
| few microseconds) before the *tmp = 0x77, then we don't see a page
| fault, even under heavy load.
A dsb() is required after modifying the PTE entries to ensure that they
will always be visible. Add this dsb().
Reported-by: Dave Hylands <dhylands@gmail.com>
Tested-by: Dave Hylands <dhylands@gmail.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
-rw-r--r-- | arch/arm/mm/dma-mapping.c | 2 |
1 files changed, 2 insertions, 0 deletions
diff --git a/arch/arm/mm/dma-mapping.c b/arch/arm/mm/dma-mapping.c index c704eed63c5..4bc43e535d3 100644 --- a/arch/arm/mm/dma-mapping.c +++ b/arch/arm/mm/dma-mapping.c @@ -229,6 +229,8 @@ __dma_alloc_remap(struct page *page, size_t size, gfp_t gfp, pgprot_t prot) } } while (size -= PAGE_SIZE); + dsb(); + return (void *)c->vm_start; } return NULL; |