[PATCH V2 04/19] mmc: mmci: Add DT bindings for signal direction

[Ulf Hansson]

On 3 April 2014 22:05, Rob Herring <robherring2 at gmail.com> wrote:
> On Mon, Mar 31, 2014 at 10:18 AM, Ulf Hansson <ulf.hansson at linaro.org> wrote:
>> Some variants have support for indicating the bus signal directions,
>> which currently are configured through platform data.
>>
>> Add corresponding DT bindings to enable us to move away from using the
>> platform data.
>>
>> Signed-off-by: Ulf Hansson <ulf.hansson at linaro.org>
>> ---
>>  Documentation/devicetree/bindings/mmc/mmci.txt |   11 ++++++++++-
>>  drivers/mmc/host/mmci.c                        |   11 +++++++++++
>>  2 files changed, 21 insertions(+), 1 deletion(-)
>>
>> diff --git a/Documentation/devicetree/bindings/mmc/mmci.txt b/Documentation/devicetree/bindings/mmc/mmci.txt
>> index ff233d1..9bd2ffa 100644
>> --- a/Documentation/devicetree/bindings/mmc/mmci.txt
>> +++ b/Documentation/devicetree/bindings/mmc/mmci.txt
>> @@ -4,7 +4,8 @@ The ARM PrimeCell MMCI PL180 and PL181 provides an interface for
>>  reading and writing to MultiMedia and SD cards alike.
>>
>>  This file documents differences between the core properties described
>> -by mmc.txt and the properties used by the mmci driver.
>> +by mmc.txt and the properties used by the mmci driver. Using "st" as
>> +the prefix for a property, indicates support by the ST Micro variant.
>>
>>  Required properties:
>>  - compatible             : contains "arm,pl18x", "arm,primecell".
>> @@ -18,6 +19,11 @@ Optional properties:
>>  - mmc-cap-sd-highspeed   : indicates whether SD is high speed capable.
>>  - vqmmc-supply           : phandle to the regulator device tree node, mentioned
>>                             as the VCCQ/VDD_IO supply in the eMMC/SD specs.
>> +- st,sig-dir-dat0        : bus signal direction pin used for DAT[0].
>> +- st,sig-dir-dat2        : bus signal direction pin used for DAT[2].
>> +- st,sig-dir-dat31       : bus signal direction pin used for DAT[3] and DAT[1].
>> +- st,sig-dir-dat74       : bus signal direction pin used for DAT[4] to DAT[7].
>> +- st,sig-dir-cmd         : cmd signal direction pin used for CMD.
>
> What I'm still not clear on is when you set these properties and when
> you don't. For example, is any combination valid and why wouldn't all
> data signals be configured the same way?

Several combinations are possible.

This is a matter of configuring the internal logic of the primecell to
which signals it shall use. That will be depending on what signal
connectors there are available on the external voltage level shifter
circuit and how you have routed these to the primecell.

The signals are used to introduce a delta delay between the external
level shifter drive enable and internal IO drive enable. It's needed
to be able to cope with the electrical parts of the SD card
specification.

Hope this answers your questions. :-)

Kind regards
Ulf Hansson

>
> Rob