[PATCH RFC 1/3] DT: bindings: mmc: Add property for 3.3V only support

On Fri, Sep 02, 2016 at 08:50:28PM +0200, Stefan Wahren wrote:

Hi Ulf, hi Rob

quoted

Ulf Hansson [off-list ref] hat am 30. August 2016 um 11:26
geschrieben:


On 18 August 2016 at 14:25, Adrian Hunter [off-list ref] wrote:

quoted

On 11/08/16 03:48, Shawn Lin wrote:

quoted

+ Adrian

Let's queue Adrian here who now maintains SDHCI stuff.

SDHCI drivers may not implement no-1-8-v in a consistent manner, but as far
as I can see, the meaning is still clear: 1.8V will not be used for either
supply or signaling.

Okay.

quoted

SDHCI is complicated because the SDHCI specification does not cover eMMC.
From the perspective of SDHCI, the only 1.8V modes are the UHS-I modes, so
support for 1.8V signaling is the same as support for one of those modes
(the spec even says as much).  But what happens is that the host controller
can support those modes but the board can't supply 1.8V so the drivers
remove capability for the modes.  Support for 1.8V supply has a capability
bit which drivers can override if necessary but removable SD cards don't
support 1.8V supply anyway, so the issue doesn't arise if the host
controller is only used for uSD cards.

By looking how SDHCI uses the SDHCI_SUPPORT_DDR50 in conjunction with
SDHCI_QUIRK2_NO_1_8_V (which is set when no-1-8-v DT property is
provided), this becomes a bit messy.

From Adrian's summary above, it then seems appropriate to limit the
no-1-8-v DT property to apply only to capabilities related to SD
cards, as I assume that also was the original purpose.

Do you think it's possible to clean up this in sdhci when assigning
the caps masks, and then also clarify the no-1-8-v DT binding in the
documentation?

was the question addressed to me? I think this clean up should be a separate
patch series. Unfortunately i don't have a clue about what exactly and how it
should be fixed.

quoted

Regarding the new DT binding proposed to be added, mmc-ddr-3_3v, it
seems we need this to be able to properly describe the HW.
Rob, do you have an issue with adding this binding? I am thinking that
we already have mmc-ddr-1_8v and mmc-ddr-1_2v, so it just follow
existing pattern.

@Rob: gently ping ...

Yes, this seems fine. I was only the no-1-8-v removal I had issue with.

Rob