From mboxrd@z Thu Jan 1 00:00:00 1970 From: Adrian Hunter Subject: Re: question about block layer and dma alignment issue. Date: Thu, 16 Oct 2014 17:31:54 +0300 Message-ID: <543FD6DA.3090703@intel.com> References: <542F9AD9.7020104@rempel-privat.de> <543027BD.5090009@kernel.dk> <5433B469.4060807@rempel-privat.de> <543405F0.4030103@kernel.dk> <5434DE9A.1030009@rempel-privat.de> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Return-path: Received: from mga01.intel.com ([192.55.52.88]:62797 "EHLO mga01.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751035AbaJPOb6 (ORCPT ); Thu, 16 Oct 2014 10:31:58 -0400 In-Reply-To: <5434DE9A.1030009@rempel-privat.de> Sender: linux-mmc-owner@vger.kernel.org List-Id: linux-mmc@vger.kernel.org To: Oleksij Rempel , Jens Axboe , "ulf.hansson@linaro.org >> Ulf Hansson" , "linux-mmc@vger.kernel.org >> linux-mmc" 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. >