Re: [PATCH v4 4/4] pwm: meson: make full use of common clock framework

[Heiner Kallweit <hkallweit1@gmail.com>]

On 16.04.2023 21:26, Martin Blumenstingl wrote:
> Hi Heiner,
> 
> On Sat, Apr 15, 2023 at 8:39 AM Heiner Kallweit <hkallweit1@gmail.com> wrote:
>>
>> On 14.04.2023 21:39, Martin Blumenstingl wrote:
>>> Hello Heiner,
>>>
>>> On Thu, Apr 13, 2023 at 7:55 AM Heiner Kallweit <hkallweit1@gmail.com> wrote:
>>> [...]
>>>> Tested-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
>>> Unfortunately I have some bad news and I need to take back my Tested-by :-(
>>> Previously my test was: cycle through all available CPU frequencies
>>> while stressing the CPU.
>>> My assumption was: if the system doesn't lock up everything's fine
>>> because we have a high enough voltage.
>>>
>>> This evening however I got a memory corruption error while trying to
>>> log in via UART - which I thought was strange.
>>> So I connected my logic analyzer to my Odroid-C1 and did some experiments:
>>>
>>> period = 30518, duty cycle = 15259 (typically used for the 32kHz
>>> output to the SDIO wifi chip)
>>> before your patches / after applying your patches:
>>> PWM: duty cycle: 50.000000% / 50.000000%
>>> PWM: period: 30.6 µs / 30.5 µs
>>> Timing: Time: 15.292 µs (65.395 kHz) / 15.250 µs (65.574 kHz)
>>> Timing: Average: 15.296 µs (65.377 kHz) / 15.264 µs (65.513 kHz)
>>> driver debug messages with your patches applied:
>>> fin_freq: 850000000 Hz
>>> period=30518 cnt=25940
>>> duty=15259 duty_cnt=12970
>>>
>>> Then I tried period = 12218, duty cycle = 0 (typically used for the
>>> highest CPU voltage):
>>> before your patches / after applying your patches:
>>> PWM: duty cycle: 0.338983% / n/a (constant low output)
>>> PWM: period: 12.3 µs / n/a
>>> Timing: Time: 12.250 µs (81.633 kHz) / n/a
>>> Timing: Average: 6.148 µs (162.668 kHz) / n/a
>>> driver debug messages with your patches applied:
>>> fin_freq: 850000000 Hz
>>> period=12218 cnt=10385
>>>
>> With a 850MHz input clock we should see a 0.01% duty cycle with 1.2ns
>> clock pulses. Can we rule out an issue with the measuring equipment?
>> Is your logic analyzer able to display such short clock pulses?
> Oh, you're right: my logic analyzer maxes out at 24MHz (~42ns).
> So we can ignore this case.
> 
>>> Finally I tried period = 12218, duty cycle = 12218 (typically used for
>>> the lowest CPU voltage):
>>> before your patches / after applying your patches:
>>> PWM: duty cycle: 99.661017% / n/a (constant low output)
> I have to correct myself: for this case my logic analyzer sees a:
> constant high signal
> 
So conclusion is that the PWM output is as expected? If yes, then the
memory corruption you saw supposedly had another root cause?
Eventually your Tested-by could be re-instantiated?

>>> PWM: period: 12.3 µs / n/a
>>> Timing: Time: 12.250 µs (81.633 kHz) / n/a
>>> Timing: Average: 6.148 µs (162.668 kHz) / n/a
>>> driver debug messages with your patches applied:
>>> fin_freq: 850000000 Hz
>>> period=12218 cnt=10385
>>>
>> Here I have no idea yet.
> [...]
>> At first I'd like to verify that the registers have the expected values.
>> Can you provide the values of PWM_A/B (depending on which channel is used in your
>> case) and PWM_MISC_AB at the end of meson_pwm_enable()? Thanks!
> I'm testing with PWM_B and I get:
>   REG_MISC_AB = 0x008000c2, channel reg = 0x28910000
> 
> This register value looks correct to me.
> 
To me as well.

> This is now my last line in meson_pwm_enable() in case you want to
> sanity-check what I did:
> dev_err(meson->chip.dev, "REG_MISC_AB = 0x%08x, channel reg = 0x%08x",
> value, readl(meson->base + channel_data->reg_offset));
> 
> 
> Best regards,
> Martin

Heiner

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