Ulf,

On Wed, Sep 2, 2015 at 4:38 AM, Ulf Hansson [off-list ref] wrote:

quoted

+/**
+ * mmc_regulator_set_vqmmc - Set VQMMC as per the ios
+ *
+ * For 3.3V signaling, we try to match VQMMC to VMMC as closely as possible.

Looking at the code, I don't think this statement is entirely true.
Isn't it so that we will be trying with a maximum tolerance of 0.3 V
towards the VMMC voltage level (then fall-back to the complete range)?
Perhaps you can find a better way to describe that in the change log.

If regulator_set_voltage_triplet() is ever implemented more correctly
then the description here is correct.  ...the problem is that
regulator_set_voltage_triplet() is still using the same shortcut that
regulator_set_voltage_tol() was using.

quoted

+int mmc_regulator_set_vqmmc(struct mmc_host *mmc, struct mmc_ios *ios)
+{
+       int volt, min_uV, max_uV;
+
+       /* If no vqmmc supply then we can't change the voltage */
+       if (IS_ERR(mmc->supply.vqmmc))
+               return -EINVAL;

In general vqmmc is considered as an optional regulator and that's
also how host drivers treat it. So perhaps it would make sense to
return 0 here instead of an error code or what do you think?

The idea is that since this is intended to be called by
start_signal_voltage_switch() and having no vqmmc should be considered
an error for start_signal_voltage_switch() then it should be an error
here.  What do you think?

quoted

+
+               /* try to stay close to vmmc at first */
+               if (!mmc_regulator_set_voltage_if_supported(mmc->supply.vqmmc,
+                                               min_uV, volt, max_uV))
+                       return 0;
+
+               return mmc_regulator_set_voltage_if_supported(mmc->supply.vqmmc,
+                                               2700000, volt, 3600000);

The whole fact that there are two calls here is really just because of
the limitations of the current implementation of
regulator_set_voltage_triplet().  If that implementation is ever fixed
then we'd just need a single call.  Probably worth a comment saying
that?