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

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Date:	Wed, 1 Jul 2015 15:45:31 +0530
From:	Vineet Gupta <Vineet.Gupta1@...opsys.com>
To:	Alexey Brodkin <Alexey.Brodkin@...opsys.com>,
	"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

On Wednesday 01 July 2015 03:32 PM, Alexey Brodkin wrote:
> 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

s/4K/8k

Alexey fat-fingered it seems. ARC cores by default have 8k MMU page size and we
saw this issue on ARC SDP boards !

-Vineet

> 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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