Re: [PATCH v2] mmc: sdhci-esdhc-imx: allow 1.8V modes without 100/200MHz pinctrl states
From: Ulf Hansson
Date: Thu Jul 05 2018 - 07:29:56 EST
>>> Btw, I still get the switching error once during boot-up:
>>> mmc1: Switching to 3.3V signalling voltage failed
>> I guess the this happens then also at system resume?
>> The core tries first with 3.3 then if it fails, it continues with 1.8V, etc.
>>> This is due to the call from mmc_set_initial_signal_voltage. It is a bit
>>> unfortunate since this is printed as a warning. Not sure if that could
>>> be prevented somehow?
>> Seems like SDHCI_SIGNALING_330 should not be set, unless 3.3V I/O is
>> supported. That should avoid SDHCI from trying and instead just
>> returning an error code immediately.
>> This seems like a generic issues for all SDHCI variant drivers.
> Hm, can we resolve this in a generic fashion?
> E.g something like this in sdhci_setup_host():
> if (!regulator_is_supported_voltage(mmc->supply.vqmmc, 3200000,
> host->flags &= ~SDHCI_SIGNALING_330;
Something like that seems right, but a wider range should be allowed.
2.7V to 3.6V is allowed according to the specs.
Also, vqmmc is optional, so in case it doesn't exist we must not clear
the SDHCI_SIGNALING_330 bit.