Messages in this thread | | | Date | Mon, 24 Nov 2014 21:29:28 -0800 | Subject | Re: [PATCH] mmc: dw_mmc: try pick the exact same voltage as vmmc for vqmmc | From | Doug Anderson <> |
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Ulf,
On Mon, Nov 24, 2014 at 5:29 AM, Ulf Hansson <ulf.hansson@linaro.org> wrote: >> 2. Several people I've talked to have expressed concerns that our >> minimum value is 2.7V. Apparently that's really on the edge and makes >> EEs a little nervous. The quick sample of cards sitting on my desk >> shows that they seem to claim 0x00ff8000, which doesn't include 2.7V. > > 0x00ff8000 states what values of VDD levels the device supports. Not VIO.
Yup, I was just pointing out that possibly others were trying to get a little bit of margin (not going all the way down to 2.7V) too.
>> Both of the above make me feel like dw_mmc should try its best to pick >> a value for vqmmc that is closest to the value of vmmc (and >= 2.7V). >> That also happens to make us work exactly like hosts where vmmc and >> vqmmc are supplied by the same supply. > > I do see your point. And I agree that it would be nice to achieve > something like this. > > The question is how to do this. For sure, we need to involve the mmc > core to handle this correctly.
You could add a function to the core that we could call from dw_mci_switch_voltage() and it would do all the work except trying to set the UHS register. That would certainly make it easy. That could try to set the highest voltage that is <= vmmc when we're at MMC_SIGNAL_VOLTAGE_330.
-Doug
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