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? -- Regards, Oleksij
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