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

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Message-ID: <88a0395b-1ab3-4ef0-96c4-440b3a5c96f4@salutedevices.com>
Date: Thu, 29 Jan 2026 17:48:17 +0300
From: George Stark <gnstark@...utedevices.com>
To: Nick Xie <nick@...das.com>
CC: "robh@...nel.org" <robh@...nel.org>, "khilman@...libre.com"
	<khilman@...libre.com>, "jbrunet@...libre.com" <jbrunet@...libre.com>,
	"martin.blumenstingl@...glemail.com" <martin.blumenstingl@...glemail.com>,
	"neil.armstrong@...aro.org" <neil.armstrong@...aro.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-amlogic@...ts.infradead.org" <linux-amlogic@...ts.infradead.org>,
	"conor+dt@...nel.org" <conor+dt@...nel.org>, "kernel@...utedevices.com"
	<kernel@...utedevices.com>, "linux-arm-kernel@...ts.infradead.org"
	<linux-arm-kernel@...ts.infradead.org>, "krzk+dt@...nel.org"
	<krzk+dt@...nel.org>, "xianwei.zhao@...ogic.com" <xianwei.zhao@...ogic.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: 回复: [DMARC error] [PATCH v3 3/3] arm64: dts: meson-s4-s905y4-khadas-vim1s: add initial device tree



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