Re: [PATCH] mmc: dw_mmc: handle data blocks > than 4kB if IDMAC is used

[Jaehoon Chung]

Hi, Alexey.

Sorry for reviewing late. i missed this patch.
I will check your patch and reply at mailing.
Thanks a lot for noticing this.

Best Regards,
Jaehoon Chung

On 07/01/2015 07:02 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@xxxxxxxxxxxx>
>> Cc: Seungwon Jeon <tgih.jun@xxxxxxxxxxx>
>> Cc: Jaehoon Chung <jh80.chung@xxxxxxxxxxx>
>> Cc: Ulf Hansson <ulf.hansson@xxxxxxxxxx>
>> Cc: arc-linux-dev@xxxxxxxxxxxx
>> Cc: linux-kernel@xxxxxxxxxxxxxxx
>> ---
>>  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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