linux-kernel - Re: [PATCH 2/3] ARM: multi_v7_defconfig: Switch BCM2835 to sdhci-iproc.c for MMC

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Date:	Fri, 1 Apr 2016 22:17:54 +0200 (CEST)
From:	Stefan Wahren <stefan.wahren@...e.com>
To:	Eric Anholt <eric@...olt.net>,
	Stephen Warren <swarren@...dotorg.org>
Cc:	Russell King <linux@....linux.org.uk>,
	linux-kernel@...r.kernel.org,
	Florian Fainelli <f.fainelli@...il.com>,
	linux-rpi-kernel@...ts.infradead.org,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 2/3] ARM: multi_v7_defconfig: Switch BCM2835 to
 sdhci-iproc.c for MMC

Hi,

> Stephen Warren <swarren@...dotorg.org> hat am 1. April 2016 um 18:58
> geschrieben:
>
>
> On 03/31/2016 08:01 PM, Stephen Warren wrote:
> > On 03/31/2016 06:28 PM, Eric Anholt wrote:
> >> This approximately triples write performance for the SD card. My card
> >> is too full of important data to collect very reliable numbers, but I
> >> see 271.361% +/- 166.742% improvement (n=3 before, 6 after), for 'dd
> >> if=/dev/zero of=/boot/asdf bs=1M count=3 oflag=dsync,direct'. Read
> >> performance appears to be unaffected.
> >
> > I thought that switching the defconfig wasn't possible, since this HW
> > module relies on the SoC core clock, and that can be asynchronously
> > changed by the FW running on the VideoCore. Consequently, this change
> > isn't safe unless the user puts non-default options in their config.txt.
> >
> > The same comment applies to "[PATCH 1/4] ARM: bcm2835: Switch BCM2835 to
> > sdhci-iproc.c for MMC" in the other series.
>
> Ah, now I realize that sdhci-bcm2835.c and sdhci-iproc.c are two
> alternative drivers for the same HW device. For some reason I got the
> incorrect impression from some past email/patch discussion that
> sdhci-iproc.c was a driver for the alternative SD controller in the chip.
>
> So, there's no problem with this patch.
> Acked-by: Stephen Warren <swarren@...dotorg.org>
>
> (although /me wonders why sdhci-iproc.c was even added in the first
> place given sdhci-bcm2835.c pre-dates it by over 2 years, and equally
> why the new driver is any faster given it looks almost identical and
> accesses the same HW, but I suppose it doesn't matter).

my old results (without DMA support) wasn't so impressing:

sdhci-bcm2835

378 kB/s WRITE
10,6 MB/s READ

sdhci-iproc

881 kB/s WRITE
10,8 MB/s READ

The performance gain comes from the more intelligent quirk handling.
sdhci-bcm2835 has a fixed delay after each write.

Regards
Stefan

>
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