[PATCH v2 3/8] mmc: core: Add mmc_regulator_set_vqmmc()

[Heiko Stübner]

Am Donnerstag, 1. Oktober 2015, 11:54:24 schrieb Ulf Hansson:
> On 30 September 2015 at 16:55, Heiko Stübner <heiko at sntech.de> wrote:
> > Am Mittwoch, 30. September 2015, 16:42:05 schrieb Ulf Hansson:
> >> On 30 September 2015 at 16:07, Heiko Stuebner <heiko at sntech.de> wrote:
> >> > From: Douglas Anderson <dianders at chromium.org>
> >> > 
> >> > This adds logic to the MMC core to set VQMMC.  This is expected to be
> >> > called by MMC drivers like dw_mmc as part of (or instead of) their
> >> > start_signal_voltage_switch() callback.
> >> > 
> >> > A few notes:
> >> > 
> >> > * When setting the signal voltage to 3.3V we do our best to make VQMMC
> >> > 
> >> >   and VMMC match.  It's been reported that this makes some old cards
> >> >   happy since they were tested back in the day before UHS when VQMMC
> >> >   and VMMC were provided by the same regulator.  A nice side effect of
> >> >   this is that we don't end up on the hairy edge of VQMMC (2.7V),
> >> >   which some EEs claim is a little too close to the minimum for
> >> >   comfort.
> >> >   This is done in two steps. At first we try to find a VQMMC within
> >> >   a 0.3V tolerance of VMMC and if this is not supported by the
> >> >   supplying regulator we try to find a suitable voltage within the
> >> >   whole 2.7V-3.6V area of the spec.
> >> > 
> >> > * The two step approach is currently necessary, as the used
> >> > 
> >> >   regulator_set_voltage_triplet(min, target, max) uses a simple
> >> >   
> >> >   implementation that just tries two basic steps:
> >> >         regulator_set_voltage(target, max);
> >> >         regulator_set_voltage(min, target);
> >> >   
> >> >   So with only one step with 2.7-3.6V borders, if a suitable voltage
> >> >   is a bit below VMMC, we would directly get the lowest 2.7V
> >> >   which some boards (like Rockchips) don't like at all.
> >> > 
> >> > * When setting the signal voltage to 1.8V or 1.2V we aim for that
> >> > 
> >> >   specific voltage instead of picking the lowest one in the range.
> >> > 
> >> > * We very purposely don't print errors in mmc_regulator_set_vqmmc().
> >> > 
> >> >   There are cases where the MMC core will try several different
> >> >   voltages and we don't want to pollute the logs.
> >> > 
> >> > Signed-off-by: Douglas Anderson <dianders at chromium.org>
> >> > Signed-off-by: Heiko Stuebner <heiko at sntech.de>
> >> 
> >> This looks good to me!
> > 
> > very cool :-)
> > 
> >> Once all are happy with the patches, can we take the mmc patches via
> >> my mmc tree or does it all have to go together?
> > 
> > The clock changes of course only touch internals of the phase-clocks, so
> > should have no problem going through another tree.
> 
> What happens if I take mmc and dt changes, wouldn't I need the clock
> patches as well?

The API stays of course the same, only the degree to settings translation gets 
optimized, so I guess in the worst case you would get no good phase and thus 
fall back to non-highspeed modes - but the system would stay running.

But of course, if the clock maintainers could Ack the two clock patches and 
everything would stay together that would work even better :-)


Heiko

> 
> > For the devicetree part I'm unsure. If the boards enable the
> > tuning-related
> > settings without the new voltage handling, 2.7V gets set on all Rockchip
> > boards which doesn't work on those at all.
> > 
> > So either the dts patches would need to go into your tree, I would need a
> > stable branch or we could simply postpone dts changes for the next cycle.
> 
> Kind regards
> Uffe