From mboxrd@z Thu Jan 1 00:00:00 1970 From: Juergen Borleis Subject: Re: [RFC] i.MX25/35/SDHCI: switch off DMA usage Date: Tue, 14 Apr 2015 11:42:00 +0200 Message-ID: <201504141142.00237.jbe@pengutronix.de> References: <201503271152.04348.jbe@pengutronix.de> <20150327114400.GA20277@shlinux1.ap.freescale.net> Mime-Version: 1.0 Content-Type: Text/Plain; charset=iso-8859-1 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: Received: from metis.ext.pengutronix.de ([92.198.50.35]:49373 "EHLO metis.ext.pengutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752479AbbDNJj2 convert rfc822-to-8bit (ORCPT ); Tue, 14 Apr 2015 05:39:28 -0400 In-Reply-To: <20150327114400.GA20277@shlinux1.ap.freescale.net> Content-Disposition: inline Sender: linux-mmc-owner@vger.kernel.org List-Id: linux-mmc@vger.kernel.org To: Dong Aisheng Cc: linux-mmc@vger.kernel.org, linux-arm-kernel@lists.infradead.org, Chris Ball , Ulf Hansson , Shawn Guo , linux-kernel@vger.kernel.org Hi, On Friday 27 March 2015 12:44:03 Dong Aisheng wrote: > On Fri, Mar 27, 2015 at 11:52:04AM +0100, Juergen Borleis wrote: > > DMA and the required overhead on very small data blocks seems an > > expensive operation. Due to erratum ENGCM07207 for i.MX25 and i.MX3= 5 SoCs > > the support for multiblock transfers is disabled which results into= a > > huge amount of single 512 byte sector transfers and interrupts. Thi= s > > slows down the transmission speed to below 500 kiB/s (even at 50 MH= z SD > > card clock). Using PIO instead of DMA to avoid ENGCM07207 happens a= nd > > re-enabling multiblock transfers again improve the transmission > > capability up to about 2.5 MiB/s. > > > > I'm still not sure if ENGCM07207 is related to DMA only and can not > > happen when PIO is used instead. Someone out there with experience > > regarding this topic? > > The errata does not state it's related to DMA only. > http://cache.freescale.com/files/dsp/doc/errata/IMX35CE.pdf > I could double check with our IC guys to confirm it. Gentle ping. Regards, Juergen --=20 Pengutronix e.K. =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0= =A0| Juergen Borleis =A0 =A0 =A0 =A0 =A0 =A0 | Industrial Linux Solutions =A0 =A0 =A0| http://www.pengut= ronix.de/ |