Re: [PATCH 3.2 047/110] stmmac: troubleshoot unexpected bits in des0 & des1
From: Alexey Brodkin <hidden>
Date: 2015-08-10 10:23:34
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Hi Ben, On Mon, 2015-08-10 at 12:12 +0200, Ben Hutchings wrote:
3.2.71-rc1 review patch. If anyone has any objections, please let me know.
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From: Alexey Brodkin <redacted>
commit f1590670ce069eefeb93916391a67643e6ad1630 upstream.
Current implementation of descriptor init procedure only takes
care about setting/clearing ownership flag in "des0"/"des1"
fields while it is perfectly possible to get unexpected bits
set because of the following factors:
[1] On driver probe underlying memory allocated with
dma_alloc_coherent() might not be zeroed and so
it will be filled with garbage.
[2] During driver operation some bits could be set by SD/MMC
controller (for example error flags etc).
And unexpected and/or randomly set flags in "des0"/"des1"
fields may lead to unpredictable behavior of GMAC DMA block.
This change addresses both items above with:
[1] Use of dma_zalloc_coherent() instead of simple
dma_alloc_coherent() to make sure allocated memory is
zeroed. That shouldn't affect performance because
this allocation only happens once on driver probe.
[2] Do explicit zeroing of both "des0" and "des1" fields
of all buffer descriptors during initialization of
DMA transfer.
And while at it fixed identation of dma_free_coherent()
counterpart as well.
Signed-off-by: Alexey Brodkin <abrodkin@synopsys.com>
Cc: Giuseppe Cavallaro <redacted>
Cc: arc-linux-dev@synopsys.com
Cc: linux-kernel@vger.kernel.org
Cc: David Miller <davem@davemloft.net>
Signed-off-by: David S. Miller <davem@davemloft.net>
[bwh: Backported to 3.2:
- Adjust context, indentation
- Normal and extended descriptors are allocated in the same place here]
Signed-off-by: Ben Hutchings <redacted>This patch looks good to me. Moreover that was exactly what I initially done on top of 3.18, see https://github.com/foss-for-synopsys-dwc-arc-processors/linux/commit/f2105b2ba9b3444568b32caca1ab253b88058fc2 So feel free to add Acked-by and/or Tested-by: Alexey Brodkin [off-list ref] -Alexey