[PATCH v2] ARM: shmobile: silk: add SDHI1 DT support

[sergei.shtylyov@cogentembedded.com (Sergei Shtylyov)]

On 08/21/2015 11:57 PM, Sergei Shtylyov wrote:

>>> Define the SILK board dependent part of the SDHI1 (connected to micro-SD slot)
>>> device nodes along with the necessary voltage regulators.
>>>
>>> Based on the original patch by Vladimir Barinov
>>> <vladimir.barinov@cogentembedded.com>.
>>>
>>> Signed-off-by: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
>>>
>>> ---
>>> This patch is against 'renesas-devel-20150810-v4.2-rc6' tag of Simon Horman's
>>> 'renesas.git' repo plus the R8A7794/SILK QSPI patches just re-posted. It needs
>>> the R8A7794 GPIO patches in order to compile.
>>>
>>> Changes in version 2:
>>> - removed not working SDHI0 stuff, renamed the patch;
>>> - replaced SDHI1's "wp-gpios" property with "disable-wp".
>>
>> I am wondering if you could explain the motivation for the "disable-wp"
>> update
>
>     Please see the comment in mmc_sd_get_ro().
>
>> and weather it is appropriate for other r8a779* dts files.
>
>     In case of micro-SD slots, yes.

    The MMC binding document says it should only be specified if the 
controller has WP detection logic. We, so far, seem to have been replying on 
the GPIOs despite this logic is present (according to the R-Car gen2 SDHI 
manuals I have). The driver will first call mmc_gpio_get_ro() and when that 
fails due to "wp-gpios" not being specified, it proceeds to reading the 
register but that is forbidden by TMIO_MMC_WRPROTECT_DISABLE flag set for the 
R-Car gen1/2 chips, so 0 is always returned from tmio_mmc_get_ro(). There 
seems to be no point in going that far (and doing the runtime PM dances) --
and MMC_CAP2_NO_WRITE_PROTECT (set when "disable-wp" is specified) prohibits 
doing that...

MBR, Sergei