Date: Thu, 3 Mar 2011 00:40:11 GMT From: Ian Lepore <freebsd@damnhippie.dyndns.org> To: freebsd-arm@FreeBSD.org Subject: Re: arm/155214: [patch] MMC/SD IO slow on Atmel ARM with modern large SD cards Message-ID: <201103030040.p230eBIt023558@freefall.freebsd.org>
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The following reply was made to PR arm/155214; it has been noted by GNATS. From: Ian Lepore <freebsd@damnhippie.dyndns.org> To: ticso@cicely.de Cc: FreeBSD-gnats-submit@freebsd.org Subject: Re: arm/155214: [patch] MMC/SD IO slow on Atmel ARM with modern large SD cards Date: Wed, 02 Mar 2011 17:21:09 -0700 On Thu, 2011-03-03 at 00:52 +0100, Bernd Walter wrote: > On Wed, Mar 02, 2011 at 02:53:18PM -0700, Ian Lepore wrote: > > > > >Number: 155214 > > >Category: arm > > >Synopsis: [patch] MMC/SD IO slow on Atmel ARM with modern large SD cards > > >Confidential: no > > >Severity: serious > > >Priority: medium > > >Responsible: freebsd-arm > > >State: open > > >Quarter: > > >Keywords: > > >Date-Required: > > >Class: sw-bug > > >Submitter-Id: current-users > > >Arrival-Date: Wed Mar 02 22:10:10 UTC 2011 > > >Closed-Date: > > >Last-Modified: > > >Originator: Ian Lepore <freebsd@damnhippie.dyndns.org> > > >Release: FreeBSD 8.2-RC3 arm > > >Organization: > > none > > >Environment: > > FreeBSD dvb 8.2-RC3 FreeBSD 8.2-RC3 #49: Tue Feb 15 22:52:14 UTC 2011 root@revolution.hippie.lan:/usr/obj/arm/usr/src/sys/DVB arm > > > > Included patch is against -current even though the problem was first seen on > > 8.2-RC3 > > > > The problem was seen on AT91RM9200 hardware, but presumably also affects the > > SAM9 series which uses the same driver code. > > > > >Description: > > With the latest generation of large-capacity SD cards, write speeds as low as > > 20 kbytes/sec are seen. These modern cards have erase-block sizes as large as > > 8192K (compared to 32K typical on previous generations). The at91_mci driver > > does only single-sector IO; apparently this requires the SD card to internally > > perform an expensive read-erase-modify-write cycle for each 512 byte block > > written to the card. > > The complete details of this problem are completely known. > However the RM9200 has many hardware problems to be worked around and > so far noone actually did. > Your patch is quite large, so I would like to ask you explicitly: > Did you test your patch with an AT91RM9200 system? > You did enable multisector support for reading and (more important) for > writing? > But you didn't activate 4bit mode? > With 4bit mode there is no hardware bug, but when the driver was written > is was just done in a lazy way because activating 4bit on SD cards require > special handling - in the meantime the SD layer itself was extracted and > has 4bit support, but the at91_mci driver was never updated to use that. > > PS: I'm very pleased to see your work since SD write speed was a > major show stopper for some applications > Yes, the patch is large, partly because I included comments about the hardware problems I found and how the code works around them (and also to help the next person understand the flow). My changes support multi-sector IO for both reads and writes. The company I work for uses the AT91RM9200 on custom-designed boards in 8 products, all with substantially similar board designs. So far we've tested these changes on 4 of them, with no problems found. I have not tested with 4-bit enabled; I wasn't aware (but in retrospect I probably should have assumed) that the hardware bugs are different with 4-bit enabled. I'm not even sure our hardware design carries all 4 lines to the card; I'll look at the schematics and if they're connected I'll see about testing that mode. (And if they're not I'll see about having our designers wire up all 4 lines on future designs.) I also haven't tested with the SAM9-series, because I don't have that hardware available. (I hope to convince our hardware designers to migrate us to SAM9 this year.)
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