On Tue, Sep 06, 2016 at 12:05:24PM -0700, Matthias Kaehlcke wrote:
> On some boards it's possible that transitioning the PWM regulator
> downwards too fast will trigger the over voltage protection (OVP) on the
> regulator. This is because until the voltage actually falls there is a
> time when the requested voltage is much lower than the actual voltage.
So your PWM regulators are not very good and overshooting? Do you have
any numbers on this - what values do you end up setting for both the
delay and safe fall percentages?
> We'll fix this OVP problem by allowing users to specify the maximum
> voltage that we can safely fall. Apparently this maximum safe voltage
> should be specified as a percentage of the current voltage. The
> regulator will then break things into separate steps with a delay in
> between.
I'd like to see some more thorough analysis than just an "apparently"
here. It's making the code more fiddly for something very handwavy.
> @@ -2753,8 +2753,6 @@ static int _regulator_do_set_voltage(struct regulator_dev *rdev,
> int old_selector = -1;
> int old_uV = _regulator_get_voltage(rdev);
>
> - trace_regulator_set_voltage(rdev_get_name(rdev), min_uV, max_uV);
> -
> min_uV += rdev->constraints->uV_offset;
> max_uV += rdev->constraints->uV_offset;
>
> @@ -2842,11 +2840,53 @@ no_delay:
> (void *)data);
> }
>
> - trace_regulator_set_voltage_complete(rdev_get_name(rdev), best_val);
> -
> return ret;
Let's remove some trace points too because...? These *are* the actual
voltage changes in the device, we're just splitting things up into a
series of transitions.
> +static int _regulator_set_voltage(struct regulator_dev *rdev,
> + int min_uV, int max_uV)
> +{
> + int safe_fall_percent = rdev->constraints->safe_fall_percent;
> + int slowest_decay_rate = rdev->constraints->slowest_decay_rate;
> + int orig_uV = _regulator_get_voltage(rdev);
> + int uV = orig_uV;
> + int ret;
> +
> + trace_regulator_set_voltage(rdev_get_name(rdev), min_uV, max_uV);
> +
> + /* If we're rising or we're falling but don't need to slow; easy */
> + if (min_uV >= uV || !safe_fall_percent)
Indentation is broken, the two lines above don't agree with each other.
> + ret = of_property_read_u32(np, "regulator-slowest-decay-rate", &pval);
> + if (!ret)
> + constraints->slowest_decay_rate = pval;
> + else
> + constraints->slowest_decay_rate = INT_MAX;
The documentation said this is mandatory if we have a safe fall rate
specified but the code says it's optional and we'll silently default to
an absurdly high rate instead (it's odd that a large number in a field
marked slowest is fast BTW). Complaining loudly seems better than
ignoring the error.
> + /* We use the value as int and as divider; sanity check */
> + if (constraints->slowest_decay_rate == 0) {
> + pr_err("%s: regulator-slowest-decay-rate must not be 0\n",
> + np->name);
> + constraints->slowest_decay_rate = INT_MAX;
> + } else if (constraints->slowest_decay_rate > INT_MAX) {
> + pr_err("%s: regulator-slowest-decay-rate (%u) too big\n",
> + np->name, constraints->slowest_decay_rate);
> + constraints->slowest_decay_rate = INT_MAX;
> + }
This should be with the parsing of slowest-decay-rate and checked only
if we have a safe-fall-percent, there's no error if the value is omitted.
> + if (constraints->safe_fall_percent > 100) {
> + pr_err("%s: regulator-safe-fall-percent (%u) > 100\n",
> + np->name, constraints->safe_fall_percent);
> + constraints->safe_fall_percent = 0;
> + }
Again indentation is borked here, I think you have tab/space issues.
> + if (constraints->safe_fall_percent &&
> + !constraints->slowest_decay_rate) {
> + pr_err("%s: regulator-slowest-decay-rate requires "
> + "regulator-safe-fall-percent\n", np->name);
Don't align the second line of the condition with the body of the if,
that just makes things hard to read - do what the rest of the code does
and align with the (.
Don't split text messages over multiple lines, it makes it impossible to
grep for the error as printed.
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