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

[Jean-Jacques Hiblot <jjhiblot@ti.com>]

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())

>
> 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.

JJ
>
> adam
>