Re: question about block layer and dma alignment issue.

[Adrian Hunter <adrian.hunter@intel.com>]

On 8/10/2014 9:50 a.m., Oleksij Rempel wrote:
> 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.

Not all cards are block devices e.g. SDIO wifi.  And there is also mmc_test.

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