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

[robh@kernel.org (Rob Herring)]

On Fri, Sep 02, 2016 at 08:50:28PM +0200, Stefan Wahren wrote:
> Hi Ulf, hi Rob
> 
> > Ulf Hansson <ulf.hansson@linaro.org> hat am 30. August 2016 um 11:26
> > geschrieben:
> > 
> > 
> > On 18 August 2016 at 14:25, Adrian Hunter <adrian.hunter@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 ...

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

Rob