From mboxrd@z Thu Jan 1 00:00:00 1970 From: Oleksij Rempel Subject: Re: question about block layer and dma alignment issue. Date: Tue, 07 Oct 2014 11:37:45 +0200 Message-ID: <5433B469.4060807@rempel-privat.de> References: <542F9AD9.7020104@rempel-privat.de> <543027BD.5090009@kernel.dk> Mime-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="IRedSEUiCwkDxqrKk34rEQWFqksxX8GMU" Return-path: Received: from mout.gmx.net ([212.227.17.22]:59934 "EHLO mout.gmx.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753676AbaJGJhx (ORCPT ); Tue, 7 Oct 2014 05:37:53 -0400 In-Reply-To: <543027BD.5090009@kernel.dk> Sender: linux-mmc-owner@vger.kernel.org List-Id: linux-mmc@vger.kernel.org To: Jens Axboe , "ulf.hansson@linaro.org >> Ulf Hansson" , "linux-mmc@vger.kernel.org >> linux-mmc" This is an OpenPGP/MIME signed message (RFC 4880 and 3156) --IRedSEUiCwkDxqrKk34rEQWFqksxX8GMU Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable 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 A= PI >> 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, b= ut >> i never had absolute aligned quarantine. >> Please tell me if i do some thing wrong or go in the wrong direction. >=20 > 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? --=20 Regards, Oleksij --IRedSEUiCwkDxqrKk34rEQWFqksxX8GMU Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- Version: GnuPG v1 iF4EAREIAAYFAlQztG0ACgkQHwImuRkmbWnTMQEAmO9SkX3JmASVTp27ujimj8hq XoHi3lPewly9XvI6g1EBAIVpbpxhKYyCu3aV8rd6YMLZiSEZuRFDRfjzQHX+ZLgr =shhp -----END PGP SIGNATURE----- --IRedSEUiCwkDxqrKk34rEQWFqksxX8GMU--