[U-Boot] PBIAS driver and MMC Interaction in U-Boot Question

[Adam Ford]

On Mon, Sep 10, 2018 at 6:40 AM Jean-Jacques Hiblot <jjhiblot at ti.com> wrote:
>
> Hi Adam,
>
>
> On 09/09/2018 14:19, Adam Ford wrote:
> > I was having some issues with a DM3730 properly reading the card
> > detect on GPIO 127 and attributed it to being related to the pbias
> > register.  I have since submitted a patch to enable GPIO_127, but I am
> > not the best approach.
> >
> > On the HSMMC driver, there are explicit commands to Disable extended
> > drain IO before changing PBIAS, because the MMC driver needs to enable
> > the PBIAS to make the MMC/SD interface operate correctly.
> >
> > I also submitted a patch to enable pbias driver found in
> > power/regulator/pbias_regulator.c to work on omap3 boards by adding
> > the 'compatible' options.   I have been able to test that the pbias
> > driver and it appears to have been setup to work on the omap3, but I
> > have only tried to read the pbias values, I haven't tried to set the
> > pbias values with it.
> >
> > Two questions:
> >
> > What I was wondering is if there is some method to get the PBIAS
> > driver to set the PBIAS instead of having the HSMMC driver do it.  It
> > seems like one should be able to do this in the device tree, but it's
> > not clear on how.
> I believe that the PBIAs must be configured by the HSMMC driver for 2
> reasons:
> * PBIAS is used by HSMMC only.
> * PBIAS must be updated when the MMC IO voltage is changed (see
> omap_hsmmc_set_io_regulator())

That function looks like it's contained in a set of #ifdef's which may
or may not be enabled.  I think it makes sense to enable it, but I
also noticed that
mmc_board_init() is manipulating the pbias settings.  Do you think
this is OK, or do you think we should remove the pbias references from
here and only
use them from omap_hsmmc_set_io_regulator()?

>
> >
> > The pbias driver does not seem to have the same checks for disabling
> > the extended drain IO before changing the PBIAS which seems to be
> > required per the DM3730 technical reference manual.  Would it make
> > sense to do this in here, or is it just better to leave it in the MMC
> > Driver?
> IMO It would make sense to do it in the PBIAS driver as it is strongly
> advised
> to toggle both at the same time.

I don't know the details of the other OMAP/Sitara SoC's, but
currently, there is an ifdef for the OMAP36XX inside mmc_board_init
which disables and enables the IO when toggling.  Are there other
SoC's that should be included and if so, do they use the same
registers?  I am basically trying to determine if the #ifdef for the
OMAP36XX is necessary or if it should always be included.

adam
>
> JJ
> >
> > adam
> >
>