linux-kernel - Re: [PATCH] mmc: dw_mmc: handle data blocks

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Date:	Wed, 1 Jul 2015 10:02:14 +0000
From:	Alexey Brodkin <Alexey.Brodkin@...opsys.com>
To:	"ulf.hansson@...aro.org" <ulf.hansson@...aro.org>,
	"jh80.chung@...sung.com" <jh80.chung@...sung.com>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>,
	"tgih.jun@...sung.com" <tgih.jun@...sung.com>,
	"arc-linux-dev@...opsys.com" <arc-linux-dev@...opsys.com>,
	Vineet Gupta <Vineet.Gupta1@...opsys.com>
Subject: Re: [PATCH] mmc: dw_mmc: handle data blocks > than 4kB if IDMAC is
 used

Hi Jaehoon, Seungwon, Ulf,

On Thu, 2015-06-25 at 11:25 +0300, Alexey Brodkin wrote:
> As per DW MobileStorage databook "each descriptor can transfer up to 
> 4kB
> of data in chained mode", moreover buffer size that is put in "des1" 
> is
> limited to 13 bits, i.e. for example on attempt to
> IDMAC_SET_BUFFER1_SIZE(desc, 8192) size value that's effectively 
> written
> will be 0.
> 
> On the platform with 8kB PAGE_SIZE I see dw_mmc gets data blocks in
> SG-list of 8kB size and that leads to unpredictable behavior of the
> SD/MMC controller.
> 
> In particular on write to FAT partition of SD-card the controller 
> will
> stuck in the middle of DMA transaction.
> 
> Solution to the problem is simple - we need to pass large (> 4kB) 
> data
> buffers to the controller via multiple descriptors. And that's what
> that change does.
> 
> What's interesting I did try original driver on same platform but
> configured with 4kB PAGE_SIZE and may confirm that data blocks passed
> in SG-list to dw_mmc never exeed 4kB limit - that explains why nobody
> ever faced a problem I did.
> 
> Signed-off-by: Alexey Brodkin <abrodkin@...opsys.com>
> Cc: Seungwon Jeon <tgih.jun@...sung.com>
> Cc: Jaehoon Chung <jh80.chung@...sung.com>
> Cc: Ulf Hansson <ulf.hansson@...aro.org>
> Cc: arc-linux-dev@...opsys.com
> Cc: linux-kernel@...r.kernel.org
> ---
>  drivers/mmc/host/dw_mmc.c | 109 ++++++++++++++++++++++++++++++------
> ----------

I'm wondering if there're any comments on that patch or if it could be
applied?

It fixes a real problem on systems on 4K PAGE_SIZE so would be good to
have it in upstream. In particular this is the case with ARC AXS board
which made its way in upstream kernel recently.

Regards,
Alexey--
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