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. -- Jens Axboe -- To unsubscribe from this list: send the line "unsubscribe linux-mmc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
