[PATCH 2/8] ARM: Implement read/write for ownership in theARMv6 DMA cache ops
catalin.marinas at arm.com
Fri May 14 12:42:31 EDT 2010
On Fri, 2010-05-14 at 17:29 +0100, Catalin Marinas wrote:
> What I think I missed in my patch (and didn't show up with a sata drive)
> is the "sync" operations. The dma_sync_single_for_device(FROMDEVICE)
> corrupts the existing buffer.
> I'll post an updated patch shortly.
Actually I think the hunk that I posted earlier should be enough:
diff --git a/arch/arm/mm/cache-v6.S b/arch/arm/mm/cache-v6.S
index a4a6840..aa3ac32 100644
@@ -216,7 +216,8 @@ v6_dma_inv_range:
- str r0, [r0] @ write for ownership
+ ldr r2, [r0] @ read for ownership
+ str r2, [r0] @ write for ownership
mcr p15, 0, r0, c7, c6, 1 @ invalidate D line
The dma_sync_single_for_cpu() eventually calls dmac_unmap_area() which
on ARM11MPCore became a no-op. There is no problem since this function
call is always preceded by a call to either dma_map_single() or
dma_sync_single_to_device(), both of them calling dma_map_area() which
does the cache invalidation.
With the patch above, v6_dma_inv_range() is no longer destructive so the
transferred data to the SDRAM is preserved. We could even re-instate the
v6_dma_unmap_area() function but for performance reasons I would leave
it as a no-op.
Russell, are you ok with such change? Since you already applied the
original patch as #6111, I will send an additional patch with this fix
(I'm sending it directly to the patch system as I won't have access to
my work PC this weekend. Feel free to apply or reject).
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