linux-kernel - Re: [PATCH 3.2 047/110] stmmac: troubleshoot unexpected bits in des0 & des1

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Date:	Mon, 10 Aug 2015 10:23:25 +0000
From:	Alexey Brodkin <Alexey.Brodkin@...opsys.com>
To:	"ben@...adent.org.uk" <ben@...adent.org.uk>
CC:	"davem@...emloft.net" <davem@...emloft.net>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"arc-linux-dev@...opsys.com" <arc-linux-dev@...opsys.com>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"peppe.cavallaro@...com" <peppe.cavallaro@...com>,
	"stable@...r.kernel.org" <stable@...r.kernel.org>
Subject: Re: [PATCH 3.2 047/110] stmmac: troubleshoot unexpected bits in
 des0 & des1

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.
> 
> ------------------
> 
> From: Alexey Brodkin <Alexey.Brodkin@...opsys.com>
> 
> 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@...opsys.com>
> Cc: Giuseppe Cavallaro <peppe.cavallaro@...com>
> Cc: arc-linux-dev@...opsys.com
> Cc: linux-kernel@...r.kernel.org
> Cc: David Miller <davem@...emloft.net>
> Signed-off-by: David S. Miller <davem@...emloft.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 <ben@...adent.org.uk>

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 <abrodkin@...opsys.com>

-Alexey--
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