Re: 回复: [DMARC error] [PATCH v3 3/3] arm64: dts: meson-s4-s905y4-khadas-vim1s: add initial device tree

[George Stark]

On 1/26/26 12:35, Nick Xie wrote:
> > Thanks for the patch. Since you have khadas mail I'm pretty sure you've
> > had the possibility to test it on the real vim board and I just don't
> > get it how it works with the voltage table above. The problem is that
> > pwm is calculated incorrectly in the upstream pwm-meson driver. That
> > voltage table appeared to be used in early amlogic bl loader and
> > appropriate pwm is initialized from a table's record. Duty cycle value
> > is translated to pwm regs correctly. Later when kernel start running
> > pwm-regulator driver is probed. It reads the pwm regs, calculates back
> > duty-cyle and search it in the table. Since calculation algos are not
> > match and the table doesn't contain full range of 0-100% values
> > regulator driver doesn't find current voltage. In such case regulator
> > core sets the minimum voltage from the table [1] and the SoC may hang
> > (depending on board) due to minimum voltage may be too low for the
> > current frequency SoC uses.
>
> I'm not sure about the PWM issues, but I checked on the real S905Y4 hardware
> and  it works.

To prove my point: run the kernel with the next patch:

diff --git a/drivers/regulator/pwm-regulator.c 
b/drivers/regulator/pwm-regulator.c
index 7434b6b22d32..14d2730b21e8 100644
--- a/drivers/regulator/pwm-regulator.c
+++ b/drivers/regulator/pwm-regulator.c
@@ -86,6 +86,9 @@ static int pwm_regulator_set_voltage_sel(struct 
regulator_dev *rdev,
        struct pwm_state pstate;
        int ret;

+       dev_info(&rdev->dev, "setting voltage from table: index: %u, uV: 
%u\n",
+               selector, drvdata->duty_cycle_table[selector].uV);
+
        pwm_init_state(drvdata->pwm, &pstate);
        pwm_set_relative_duty_cycle(&pstate,
                        drvdata->duty_cycle_table[selector].dutycycle, 
100);

In dmesg there must be a message like "setting voltage from table: 
index: 36, uV: 689000"
If to take a look at operation points table for s4 in vendor kernels the 
lowest voltage is 0.769V for 100Mhz
so setting 689000uV even temporary may lead to problems depending on 
particular hardware.

> > Or I'm missing something?
>
>
> > There's not-yet-reviewed patch that fixes pwm algo [2]. There's
> > calculation example in the cover letter.
> > [1] https://elixir.bootlin.com/linux/v6.19-rc5/source/drivers/regulator/core.c#L1227
> > [2] https://lkml.iu.edu/2412.3/00826.html
>
> What's the status of such patches?

the patch is ready for review. It's seems like nobody is interested

> --
>
> Best regards
>
> George

--
Best regards
George