On 2019-02-26 8:23 pm, Nicolin Chen wrote:
This reverts commit d222e42e88168fd67e6d131984b86477af1fc256.
The original change breaks omap dss:
omapdss_dispc 58001000.dispc:
dispc_errata_i734_wa_init: dma_alloc_writecombine failed
Let's revert it first and then find a safer solution instead.
Ah, I think I see the problem - once arch/arm's __dma_alloc() has
decided to use CMA (because dev_get_cma_area(dev) returns the global
area), it then won't fall back to trying a regular page allocation if
dma_alloc_from_contiguous() returns NULL. Thus anything on 32-bit Arm
trying to allocate a single-page buffer in blockable context with a
CMA-enabled config is just going to fail. Similarly, it looks like none
of the DMA_ATTR_FORCE_CONTIGUOUS cases are prepared to handle this
change either (amd_iommu appears technically affected, but is already
using dma_alloc_from_contiguous() backwards compared to everyone else, hmm).
I guess the question is whether to add alloc_page()/free_page()
fallbacks to those call sites, or stuff them directly into the CMA
helpers here.
Robin.
Reported-by: Tony Lindgren <t...@atomide.com>
Signed-off-by: Nicolin Chen <nicoleots...@gmail.com>
---
Tony,
Would you please test and verify? Thanks!
kernel/dma/contiguous.c | 22 +++-------------------
1 file changed, 3 insertions(+), 19 deletions(-)
diff --git a/kernel/dma/contiguous.c b/kernel/dma/contiguous.c
index 09074bd04793..b2a87905846d 100644
--- a/kernel/dma/contiguous.c
+++ b/kernel/dma/contiguous.c
@@ -186,32 +186,16 @@ int __init dma_contiguous_reserve_area(phys_addr_t size,
phys_addr_t base,
*
* This function allocates memory buffer for specified device. It uses
* device specific contiguous memory area if available or the default
- * global one.
- *
- * However, it skips one-page size of allocations from the global area.
- * As the addresses within one page are always contiguous, so there is
- * no need to waste CMA pages for that kind; it also helps reduce the
- * fragmentations in the CMA area. So a caller should be the rebounder
- * in such case to allocate a normal page upon NULL return value.
- *
- * Requires architecture specific dev_get_cma_area() helper function.
+ * global one. Requires architecture specific dev_get_cma_area() helper
+ * function.
*/
struct page *dma_alloc_from_contiguous(struct device *dev, size_t count,
unsigned int align, bool no_warn)
{
- struct cma *cma;
-
if (align > CONFIG_CMA_ALIGNMENT)
align = CONFIG_CMA_ALIGNMENT;
- if (dev && dev->cma_area)
- cma = dev->cma_area;
- else if (count > 1)
- cma = dma_contiguous_default_area;
- else
- return NULL;
-
- return cma_alloc(cma, count, align, no_warn);
+ return cma_alloc(dev_get_cma_area(dev), count, align, no_warn);
}
/**
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