[1/2] dt-bindings: mmc: Document no-uhs-voltage MMC property

Add documentation for no-uhs-voltage MMC property.

Signed-off-by: Marek Behún <marek.behun@nic.cz>
Cc: Rob Herring <robh+dt@kernel.org>
Cc: devicetree@vger.kernel.org
---
 Documentation/devicetree/bindings/mmc/mmc.txt | 1 +
 1 file changed, 1 insertion(+)

On 18 October 2018 at 17:29, Marek Behún <marek.behun@nic.cz> wrote:
> Add documentation for no-uhs-voltage MMC property.
>
> Signed-off-by: Marek Behún <marek.behun@nic.cz>
> Cc: Rob Herring <robh+dt@kernel.org>
> Cc: devicetree@vger.kernel.org
> ---
>  Documentation/devicetree/bindings/mmc/mmc.txt | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/Documentation/devicetree/bindings/mmc/mmc.txt b/Documentation/devicetree/bindings/mmc/mmc.txt
> index f5a0923b34ca..0506dcbc2070 100644
> --- a/Documentation/devicetree/bindings/mmc/mmc.txt
> +++ b/Documentation/devicetree/bindings/mmc/mmc.txt
> @@ -55,6 +55,7 @@ Optional properties:
>  - no-sdio: controller is limited to send sdio cmd during initialization
>  - no-sd: controller is limited to send sd cmd during initialization
>  - no-mmc: controller is limited to send mmc cmd during initialization
> +- no-uhs-voltage: controller does not support switching to UHS voltage

We already have bindings for telling which UHS modes that are supported.

It doesn't make sense to me, to also have a binding saying that UHS
mode isn't supported, as that information is already available.

>  - fixed-emmc-driver-type: for non-removable eMMC, enforce this driver type.
>    The value <n> is the driver type as specified in the eMMC specification
>    (table 206 in spec version 5.1).
> --
> 2.18.1
>

Kind regards
Uffe

On Mon, 22 Oct 2018 14:23:04 +0200
Ulf Hansson <ulf.hansson@linaro.org> wrote:

> On 18 October 2018 at 17:29, Marek Behún <marek.behun@nic.cz> wrote:
> > Add documentation for no-uhs-voltage MMC property.
> >
> > Signed-off-by: Marek Behún <marek.behun@nic.cz>
> > Cc: Rob Herring <robh+dt@kernel.org>
> > Cc: devicetree@vger.kernel.org
> > ---
> >  Documentation/devicetree/bindings/mmc/mmc.txt | 1 +
> >  1 file changed, 1 insertion(+)
> >
> > diff --git a/Documentation/devicetree/bindings/mmc/mmc.txt
> > b/Documentation/devicetree/bindings/mmc/mmc.txt index
> > f5a0923b34ca..0506dcbc2070 100644 ---
> > a/Documentation/devicetree/bindings/mmc/mmc.txt +++
> > b/Documentation/devicetree/bindings/mmc/mmc.txt @@ -55,6 +55,7 @@
> > Optional properties:
> >  - no-sdio: controller is limited to send sdio cmd during
> > initialization
> >  - no-sd: controller is limited to send sd cmd during initialization
> >  - no-mmc: controller is limited to send mmc cmd during
> > initialization +- no-uhs-voltage: controller does not support
> > switching to UHS voltage  
> 
> We already have bindings for telling which UHS modes that are
> supported.
> 
> It doesn't make sense to me, to also have a binding saying that UHS
> mode isn't supported, as that information is already available.
> 

Hi Ulf,
the problem here is that I some boards have hardware bugs which report
UHS support but the voltage switch won't work. In this case how should
I tell the kernel not to do the voltage_switch? If I looked at the code
correctly, currently there isn't a way to specify this via device tree.

sd.c function mmc_sd_get_cid calls mmc_set_uhs_voltage if the device
reports it (CCS and S18A in the response is set). But
mmc_set_uhs_voltage fails on such boards and kernel won't boot root
partition.

Marek