linux-kernel - Re: Nokia N900: u-SD card in v4.2+

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Message-ID: <20160113191240.GA10717@amd>
Date:	Wed, 13 Jan 2016 20:12:40 +0100
From:	Pavel Machek <pavel@....cz>
To:	Kishon Vijay Abraham I <kishon@...com>
Cc:	Pali Rohár <pali.rohar@...il.com>,
	tony@...mide.com, sre@...ian.org, sre@...g0.de,
	kernel list <linux-kernel@...r.kernel.org>,
	linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
	linux-omap@...r.kernel.org, khilman@...nel.org,
	aaro.koskinen@....fi, ivo.g.dimitrov.75@...il.com,
	patrikbachan@...il.com
Subject: Re: Nokia N900: u-SD card in v4.2+

On Mon 2016-01-11 14:10:23, Kishon Vijay Abraham I wrote:
> Hi,
> 
> On Sunday 10 January 2016 04:14 AM, Pali Rohár wrote:
> > On Thursday 07 January 2016 12:34:09 Pavel Machek wrote:
> >> Hi!
> >>
> >>> On Thursday 07 January 2016 02:16 AM, Pavel Machek wrote:
> >>>> Hi!
> >>>>
> >>>> In v4.1, both internal MMC and u-SD cards work ok.
> >>>>
> >>>> In v4.2, only the internal MMC is detected. In v4.3, not even
> >>>> internal MMC works. In v4.4, only the internal MMC is detected.
> >>>>
> >>>> Does it work for you? Any patches?
> >>>
> >>> I don't have Nokia N900 to check this, but can you share your
> >>> config and kernel logs? Check if CONFIG_REGULATOR_PBIAS is present
> >>> in your config. CONFIG_REGULATOR_PBIAS is now mandatory for all
> >>> omap3+ SoCs to work.
> >>
> >> I enabled CONFIG_REGULATOR_PBIAS and both MMCs now work.
> >>
> >> I wonder if we should add some selects, so that users updating from
> >> old kernels don't break their system?
> > 
> > Please add these selects. I had CONFIG_REGULATOR_PBIAS disabled too, 
> > because I just updated defconfig from older kernel version.
> 
> 'select' is generally not recommended since it selects a config without
> caring for the dependency. With adding 'depends on', MMC won't be enabled and
> will end up in the same problem.

Well... it really should "depend on". Not ideal, but you'll likely
realize what went on.

Silently compiling known-bad kernel is ... well.. bad.

> Tony has already added a Documentation noting that CONFIG_REGULATOR_PBIAS
> should be enabled for MMCs to work.
> commit d8e1f5ed11a39a68da00f05000466c4f6db4456e
> Author: Tony Lindgren <tony@...mide.com>
> Date:   Mon Oct 12 16:19:54 2015 -0700
> 
>     Documentation: ARM: List new omap MMC requirements
> 
> Maybe we should also make the error message a little more verbose to tell the
> user that CONFIG_REGULATOR_PBIAS be selected?

That would help.

As would #error if we recognize broken config.
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html