Re: [PATCH/RFC] mmc: sh_mmcif: revision-specific configuration from Device Tree

[Chris Ball <cjb@laptop.org>]

Hi Guennadi,

On Mon, Aug 05 2013, Guennadi Liakhovetski wrote:
> Add compatibility strings to configure MMCIF revision-specific features.
> MMCIF blocks are always integrated into SoCs, so, we use SoC model to
> distinguish between MMCIF versions.
>
> Signed-off-by: Guennadi Liakhovetski <g.liakhovetski+renesas@gmail.com>
> ---
>
> Hi Chris,
> I marked this as RFC, because having no access to the MMC standard I'm not 
> certain about VccQ requirements for MMC DDR. On the one hand a comment in 
> mmc.c says
> 	 * EXT_CSD_CARD_TYPE_DDR_1_8V means 3.3V or 1.8V vccq.
> which suggests, that DDR (DDR50?) can be used with VccQ = 3.3V, 1.8V and 
> 1.2V at least. But in mmc_init_card() DDR50 is only requested from the 
> driver if either MMC_CAP_1_8V_DDR or MMC_CAP_1_2V_DDR is specified in 
> host's capabilities. So, I'm actually not sure whether MMC_CAP_UHS_DDR50 
> alone without 1_8V or 1_2V makes sense. That's also what I implemented in 
> this patch - DDR50 is only enabled in combination with either 1.2 or 1.8V 
> capability. Is this correct?

OLPC's using DDR50 at 3.3V in production.  Honestly, I don't know
whether it's spec compliant (I think the spec claims that 1.8V is
required) but it happens to work on these parts.  The host controller
does support 1.8V, there's just no hardware capable of supplying 1.8V
to MMC on the board.

Thanks,

- Chris.
-- 
Chris Ball   <cjb@laptop.org>   <http://printf.net/>ng