Re: [PATCH/RFC] mmc: add DT bindings for more MMC capability flags

[Arnd Bergmann <arnd@arndb.de>]

On Wednesday 06 February 2013, Guennadi Liakhovetski wrote:
> 
> On Thu, 7 Feb 2013, Arnd Bergmann wrote:
> 
> > On Wednesday 06 February 2013 17:25:42 Guennadi Liakhovetski wrote:
> > > 
> > > Thank for pointing me out at that thread. However, I don't think 
> > > MMC_CAP_POWER_OFF_CARD has anything to do with compatibility or hardware 
> > > revisions. At least I haven't yet come across any sd/mmc hosts, that also 
> > > supply card power. You could "derive" this flag from the presence of a 
> > > regulator, capable of changing its status (switching on / off), but even 
> > > then you're not guaranteed, that you actually can (and want to) power the 
> > > card off at run-time - the regulator can be shared etc. So, an explicit 
> > > flag is needed.
> > 
> > It sounds like something that should be handled in a controller specific
> > way I think. E.g. on SDHCI, there seems to always be a method to power
> > down the card using the SDHCI_POWER_CONTROL register, even without
> > any external regulators.
> 
> If I understand correctly, that register only controls card bus power. 
> Further sdhci.c uses regulators (host->vmmc) to power up and down the 
> card.

Ok, that may be true. So a device that can only power down the bus
but not the card itself should not set MMC_CAP_POWER_OFF_CARD
then? I only saw that it is set unconditionally for the PCI
case, which does not use regulators.

	Arnd