linux-kernel - Re: [PATCH RFC] ARM: dts: mxs: leave card detect out of common mmc pins config

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Date:	Mon, 8 Apr 2013 15:58:05 +0200
From:	Hector Palacios <hector.palacios@...i.com>
To:	Shawn Guo <shawn.guo@...aro.org>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"maxime.ripard@...e-electrons.com" <maxime.ripard@...e-electrons.com>,
	"marex@...x.de" <marex@...x.de>,
	"fabio.estevam@...escale.com" <fabio.estevam@...escale.com>
Subject: Re: [PATCH RFC] ARM: dts: mxs: leave card detect out of common mmc
 pins config

On 04/08/2013 02:48 PM, Shawn Guo wrote:
> On Mon, Apr 08, 2013 at 12:12:20PM +0200, Hector Palacios wrote:
>> MicroSD card sockets don't usually have card detect line. This pin
>> is actually not needed for the MMC to work and it is more of a
>> platform design decission to have it.
>> The card detect pin already has a configuration entry of its own:
>> 'mmc0_cd_cfg' so we complete the iomux configuration here and let
>> platforms to include it or not depending on whether the card detect
>> line is routed to the SD socket.
>>
> Sounds sensible.
>
>> Signed-off-by: Hector Palacios <hector.palacios@...i.com>
>> ---
>>
>> Hello,
>>
>> All imx28 based platforms except 'bluegiga,apx4devkit' and
>> 'schulercontrol,imx28-sps1', use 'mmc0_cd_cfg' in their mmc configuration
>> so please check whether this patch would break these platforms.
>>
> I just tested the patch on imx28-evk and card-detection still works.  So
> patches applied, thanks.

The EVK and most platforms will work because they are using 'mmc0_cd_cfg' so actually 
this patch does not change anything on them.
Platforms 'bluegiga,apx4devkit' and 'schulercontrol,imx28-sps1' however are not 
referencing 'mmc0_cd_cfg' so after applying this patch they will have unconfigured CD 
line and they may break.
The driver will call get_cd() upon probing, which returns the status of the CD line.
Please check these two platforms before applying.

In fact I was looking now at how to skip the calling of get_cd() hook when you specify 
'non-removable' in the Device Tree. According to the bindings document:

   - non-removable: non-removable slot (like eMMC); *assume always present.*

This property is not handled in mxs-mmc.c but even if I add the code to handle it and 
set MMC_CAP_NONREMOVABLE flag, the get_cd() is called at least once and returning with 
the status of CD line. I think this is wrong because it should assume the card is 
present. The CD line may not be connected at all and may have any value.

Regards,
-- 
Héctor Palacios
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