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

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Message-ID: <56936A77.9070803@ti.com>
Date:	Mon, 11 Jan 2016 14:10:23 +0530
From:	Kishon Vijay Abraham I <kishon@...com>
To:	Pali Rohár <pali.rohar@...il.com>,
	Pavel Machek <pavel@....cz>, <tony@...mide.com>
CC:	<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+

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.

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?

Thanks
Kishon