On Tue, Nov 20, 2012 at 2:53 AM, Johan Rudholm <jrudholm@xxxxxxxxx> wrote:
>> On the other hand, we may have a good basis to add a quirk, triggered
>> by the device tree, for when the hardware physically does not have
>> 1.8v capabilities.
>
> This also seems proper, if we know we can't get 1.8V, then we
> shouldn't even try for it. In this way the detection will also be
> faster (no 10 retries).
I've gone for this approach in the patches just posted.
sdhci: add quirk for lack of 1.8v support
mmc: add no-1-8-v device tree flag
>> If this is the case, the driver could have another heuristic: if there
>> is no vmmc regulator, there is no way of cutting the card power,
>> therefore we could avoid even trying 1.8v on the basis that we know we
>> can't recover if things go wrong.
>
> So the driver could for instance drop the MMC_CAP_UHS_DDR50 cap if
> there is no way to power cycle the card? I think that sounds
> reasonable and according to spec, although also a little bit hard
> since there probably are cards out there that never require a power
> cycle to perform a proper voltage switch?
Thats true, and actually, after some more investigation it doesn't
seem like we have a solid basis to add such behaviour. It looks like
whether or not the voltage supply is supplied by the same chip that
provides the SDHCI interface, or whether it is a purely external
factor, varies from board to board. So we can't assume a lack of
regulator means a lack of ability to switch voltages.
Thanks
Daniel
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