Messages in this thread Patch in this message | ![/](/images/icornerl.gif) | | From | Martin Blumenstingl <> | Subject | [RFC PATCH v1] regulator: pwm-regulator: Fix continuous get_voltage for disabled PWM | Date | Thu, 21 Dec 2023 22:12:22 +0100 |
| |
Odroid-C1 uses a Monolithic Power Systems MP2161 controlled via PWM for the VDDEE voltage supply of the Meson8b SoC. Commit 6b9352f3f8a1 ("pwm: meson: modify and simplify calculation in meson_pwm_get_state") results in my Odroid-C1 crashing with memory corruption in many different places (seemingly at random). It turns out that this is due to a currently not supported corner case.
The VDDEE regulator can generate between 860mV (duty cycle of ~91%) and 1140mV (duty cycle of 0%). We consider it to be enabled by the bootloader (which is why it has the regulator-boot-on flag in .dts) as well as being always-on (which is why it has the regulator-always-on flag in .dts) because the VDDEE voltage is required for the Meson8b SoC to work. The public S805 datasheet [0] states on page 17 (where "A5" refers to the Cortex-A5 CPU cores): [...] So if EE domains is shut off, A5 memory is also shut off. That does not matter. Before EE power domain is shut off, A5 should be shut off at first.
It turns out that at least some bootloader versions are keeping the PWM output disabled. This is not a problem due to the specific design of the regulator: when the PWM output is disabled the output pin is pulled LOW, effectively achieving a 0% duty cycle (which in return means that VDDEE voltage is at 1140mV).
The problem comes when the pwm-regulator driver tries to initialize the PWM output. To do so it reads the current state from the hardware, which is: period: 3666ns duty cycle: 3333ns (= ~91%) enabled: false Then those values are translated using the continuous voltage range to 860mV. Later, when the regulator is being enabled (either by the regulator core due to the always-on flag or first consumer - in this case the lima driver for the Mali-450 GPU) the pwm-regulator driver tries to keep the voltage (at 860mV) and just enable the PWM output. This is when things start to go wrong as the typical voltage used for VDDEE is 1100mV.
Commit 6b9352f3f8a1 ("pwm: meson: modify and simplify calculation in meson_pwm_get_state") triggers above condition as before that change period and duty cycle were both at 0. Since the change to the pwm-meson driver is considered correct the solution is to be found in the pwm-regulator driver which now considers the voltage to be at the minimum or maximum (depending on whether the polarity is inverted) if the PWM output is disabled. This makes the VDDEE regulator on Odroid-C1 read 1140mV while the PWM output is disabled, so all following steps try to keep the 1140mV until any regulator consumer (such as the lima driver's devfreq implementation) tries to set a different voltage (1100mV is the target voltage).
[0] https://dn.odroid.com/S805/Datasheet/S805_Datasheet%20V0.8%2020150126.pdf
Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com> --- Sending this as RFC as I'm not 100% sure if this is the correct way to solve my problem. Reverting commit 6b9352f3f8a1 (which I found via git bisect) also works, but it seems hacky.
Once we agreed on the "correct" solution I will add Fixes tags as needed
drivers/regulator/pwm-regulator.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-)
diff --git a/drivers/regulator/pwm-regulator.c b/drivers/regulator/pwm-regulator.c index 2aff6db748e2..30402ee18392 100644 --- a/drivers/regulator/pwm-regulator.c +++ b/drivers/regulator/pwm-regulator.c @@ -157,7 +157,12 @@ static int pwm_regulator_get_voltage(struct regulator_dev *rdev) pwm_get_state(drvdata->pwm, &pstate); - voltage = pwm_get_relative_duty_cycle(&pstate, duty_unit); + if (pstate.enabled) + voltage = pwm_get_relative_duty_cycle(&pstate, duty_unit); + else if (max_uV_duty < min_uV_duty) + voltage = max_uV_duty; + else + voltage = min_uV_duty; /* * The dutycycle for min_uV might be greater than the one for max_uV. -- 2.43.0
| ![\](/images/icornerr.gif) |