linux-kernel - Re: [PATCH 2/2] mmc: Test bus-width for old MMC devices

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Message-ID: <s5h1v5wv6gv.wl%tiwai@suse.de>
Date:	Sun, 05 Dec 2010 11:50:40 +0100
From:	Takashi Iwai <tiwai@...e.de>
To:	Chris Ball <cjb@...top.org>
Cc:	Philip Rakity <prakity@...vell.com>, linux-mmc@...r.kernel.org,
	linux-kernel@...r.kernel.org, Aries Lee <arieslee@...cron.com>
Subject: Re: [PATCH 2/2] mmc: Test bus-width for old MMC devices

Hi Chris,

At Sun, 5 Dec 2010 04:02:24 +0000,
Chris Ball wrote:
> 
> Hi Takashi, Philip,
> 
> On Wed, Nov 24, 2010 at 07:21:14AM +0100, Takashi Iwai wrote:
> > From: Aries Lee <arieslee@...cron.com>
> > 
> > Some old MMC devices fail with the 4/8 bits the driver tries to use
> > exclusively.  This patch adds a test for the given bus setup and falls
> > back to the lower bit mode (until 1-bit mode) when the test fails.
> > 
> > [Major rework and refactoring by tiwai]
> > 
> > Signed-off-by: Aries Lee <arieslee@...cron.com>
> > Signed-off-by: Takashi Iwai <tiwai@...e.de>
> 
> We have two independent patches for performing MMC bus-width testing now:
> 
>   https://patchwork.kernel.org/patch/351781/
>   https://patchwork.kernel.org/patch/361702/

Yeah, Philip and I discussed shortly in a mail thread after that.

> I'm planning on taking Takashi's since it looks a little cleaner; Philip,
> please could you take a look at Takashi's patch and add anything you
> think should be present from your own patch as a new incremental patch?

One missing thing in my (originally Aries') patch is the quirk bit to
enable/disable the bus-width test.  In Philip's latest patch, the
default is off.

I'm also not sure whether this bus-width test should be enabled as
default.  I guess it's better for performance, so I'd vote for turning
on as default.  But, having a quirk for turning off would be safer for
working around old hardware problems, of course.


thanks,

Takashi
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