[lkml]   [2020]   [Sep]   [28]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
Patch in this message
SubjectRe: [PATCH 05/18] ARM/dma-mapping: Switch to iommu_dma_ops
Hi Robin,

On 20.08.2020 17:08, Robin Murphy wrote:
> With the IOMMU ops now looking much the same shape as iommu_dma_ops,
> switch them out in favour of the iommu-dma library, currently enhanced
> with temporary workarounds that allow it to also sit underneath the
> arch-specific API. With that in place, we can now start converting the
> remaining IOMMU drivers and consumers to work with IOMMU API default
> domains instead.
> Signed-off-by: Robin Murphy <>

I've played a bit longer with this and found that reading the kernel
virtual address of the buffers allocated via dma_alloc_attrs() from
dma-iommu ops gives trashes from time to time. It took me a while to
debug this...

Your conversion misses adding arch_dma_prep_coherent() to arch/arm, so
the buffers are cleared by the mm allocator, but the caches are NOT
flushed for the newly allocated buffers.

This fixes the issue:

diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index fec3e59215b8..8b60bcc5b14f 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -2,6 +2,7 @@
 config ARM
        default y
        select ARCH_32BIT_OFF_T
        select ARCH_HAS_BINFMT_FLAT
        select ARCH_HAS_DEBUG_VIRTUAL if MMU
diff --git a/arch/arm/mm/dma-mapping.c b/arch/arm/mm/dma-mapping.c
index ff6c4962161a..6954681b73da 100644
--- a/arch/arm/mm/dma-mapping.c
+++ b/arch/arm/mm/dma-mapping.c
@@ -266,6 +266,20 @@ static void __dma_clear_buffer(struct page *page,
size_t size, int coherent_flag

+void arch_dma_prep_coherent(struct page *page, size_t size)
+       if (PageHighMem(page)) {
+               phys_addr_t base = __pfn_to_phys(page_to_pfn(page));
+               phys_addr_t end = base + size;
+               outer_flush_range(base, end);
+       } else {
+               void *ptr = page_address(page);
+               dmac_flush_range(ptr, ptr + size);
+               outer_flush_range(__pa(ptr), __pa(ptr) + size);
+       }
  * Allocate a DMA buffer for 'dev' of size 'size' using the
  * specified gfp mask.  Note that 'size' must be page aligned.
I also wonder if it would be better to use per-arch __dma_clear_buffer()
instead of setting __GFP_ZERO unconditionally in dma-iommu.c. This
should be faster on ARM with highmem...

> ...

Best regards
Marek Szyprowski, PhD
Samsung R&D Institute Poland

 \ /
  Last update: 2020-09-28 13:33    [W:0.260 / U:0.484 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site