Re: [BUG] mmc_regulator_set_ocr can't cope with regulator-fixed

From: Ravikumar Kattekola
Date: Fri Aug 06 2021 - 04:15:19 EST

Resending my reply as my Mail client settings prevented delivery

On 05/08/21 6:38 pm, Mark Brown wrote:
On Thu, Aug 05, 2021 at 08:58:58AM -0400, Peter Geis wrote:
On Thu, Aug 5, 2021 at 8:47 AM Mark Brown <broonie@xxxxxxxxxx> wrote:

One thing to watch out for with this approach is if there's things that
really need a specific voltage to be set then you'll have to stop those
things happening if you've got a voltage regulator that can't deliver a
voltage in the required range. I don't know if this affects MMC or not,
if it's just a case of being less efficient it's not such an issue.

Yeah, but if this is a fixed regulator and it's a problem, then the
hardware is screwed anyways.

Well, the fact that the voltage is being changed at runtime indicates
that we're changing something from whatever was in the fixed setup - it
can sometimes be that we don't have access to some higher performance or
lower power features for example. That's not ideal but works perfectly

Suggested approach of checking "mmc->ocr_avail" might work.

But, IMO mmc core should check if the voltage can be changed or not

before trying to do regulator_set_voltage() in mmc_regulator_set_ocr().

Wouldn't that be better and solve this issue for other hosts as well.

Something like below in mmc_regulator_set_ocr ():

+ result = regulator_check_voltage_constraints(supply,
+ min_uV, max_uV);
+ if(!result) {
+ result = regulator_set_voltage(supply, min_uV, max_uV);
+ if (result != -EINVAL && !mmc->regulator_enabled) {
+ result = regulator_enable(supply);
+ if (!result)
+ mmc->regulator_enabled = true;
+ }

We could wrap the existing check_voltage function

+/* Check voltage constraints helper function */
+int regulator_check_voltage_constraints(struct regulator *regulator,
+ int min_uV, int max_uV)
+ return regulator_check_voltage(regulator->rdev, &min_uV, &max_uV);

I hope this makes sense.