Re: question about block layer and dma alignment issue.

[Oleksij Rempel <linux@rempel-privat.de>]

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Am 07.10.2014 um 17:25 schrieb Jens Axboe:
> On 10/07/2014 03:37 AM, Oleksij Rempel wrote:
>> Am 04.10.2014 um 19:00 schrieb Jens Axboe:
>>> On 2014-10-04 00:59, Oleksij Rempel wrote:
>>>> Hello Jens,
>>>>
>>>> i hope it is OK to ask you directly, i didn't found better way to do
>>>> this.
>>>> I'm writing MMC driver based on reverse engineering for au6601 mmc
>>>> controller. This driver uses MMC API, and last one trying to use BLK API
>>>> as directly as possible. So far so gut, but i have a problem by using SG
>>>> requests with DMA without conversation. This controller accepts only
>>>> addresses with this mask 0xffff.f000 - also page aligned.
>>>> Till now i tried different QUEUE_FLAG_ flags and blk_queue settings, but
>>>> i never had absolute aligned quarantine.
>>>> Please tell me if i do some thing wrong or go in the wrong direction.
>>>
>>> Unless you can accept a 4kb hardware block size (and I'm assuming you
>>> cannot, since you need to support 512b file systems?), then you'd have
>>> to bounce the requests that don't align properly. You can fix some of
>>> them by setting blk_queue_dma_alignment(q, 4095).
>>
>> I needed to include MMC list with Ulf Hansson at the beginning, so here
>> we are.
>>
>> Hi Ulf,
>>
>> here is the list of drivers which do care about dma alignment . Some of
>> them use bounce_buffer, some will use PIO instead of DMA, for not
>> aligned requests:
>>
>> dw_mmc.c: dw_mci_pre_dma_transfer
>> wbsd.c
>> usdhi6rol0.c
>> tmio_mmc_dma.c
>> sunxi-mmc.c
>> sdhci.c
>> pxamci.c
>> mvsdio.c
>> au6601.c(not upstream jet)
>>
>> The problem of all this driver is that each of them use own solution. I
>> think this code can be moved to some common place. For example, it can
>> be done in drivers/mmc/card/queue.c and enabled by
>> mmc_host_dma_alignment variable. Or provide a mmc_sg_align() function,
>> which should be called explicatively by driver.
>>
>> Which option is preferable?
> 
> I would roll a block version that they all can use, you can look at
> block/bounce.c for inspiration. That file deals with bouncing higher
> pages to lower memory, so it's not exactly what you want. But the metod
> of allocating a new bio that meets criteria and copying data over, that
> is the same that you need.

Ok,

i will need to setup testing board for this kind of work. It will take
some time.

-- 
Regards,
Oleksij


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