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

[Stefan Wahren]

Hi Ulf, hi Rob

> Ulf Hansson <ulf.hansson at linaro.org> hat am 30. August 2016 um 11:26
> geschrieben:
> 
> 
> On 18 August 2016 at 14:25, Adrian Hunter <adrian.hunter at intel.com> wrote:
> > On 11/08/16 03:48, Shawn Lin wrote:
> >> + 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.
> 
> >
> > 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.

> 
> 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 ...

Regards
Stefan

> 
> [...]
> 
> Kind regards
> Uffe
> 
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