Messages in this thread | | | Subject | Re: [PATCH 0/2] Change PWM-controlled LED pin active mode and algorithm | From | Ron Economos <> | Date | Tue, 17 Jan 2023 17:46:41 -0800 |
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On 1/17/23 7:08 AM, Ron Economos wrote: > On 1/17/23 1:32 AM, Nylon Chen wrote: >> Hi Conor, Jessica >> >> thanks for your reply. >> >> Jessica Clarke <jrtc27@jrtc27.com> 於 2023年1月14日 週六 上午3:24寫道: >>> On 13 Jan 2023, at 18:32, Conor Dooley <conor@kernel.org> wrote: >>>> +CC Uwe, Thierry, linux-pwm >>>> >>>> Hey Nylon, >>>> >>>> Please run scripts/get_maintainer.pl before sending patches, you >>>> missed >>>> both me & the PWM maintainers unfortunately! >>>> AFAIK, the PWM maintainers use patchwork, so you will probably have to >>>> resend this patchset so that it is on their radar. >>>> I've marked the series as "Changes Requested" on the RISC-V one. >> I got it. I will base it on get_maintainer.pl, re-sent it. >>>> On Fri, Jan 13, 2023 at 04:31:13PM +0800, Nylon Chen wrote: >>>> >>>>> According to the circuit diagram of User LEDs - RGB described in the >>>>> manual hifive-unmatched-schematics-v3.pdf[0]. >>>>> The behavior of PWM is acitve-high. >>>>> >>>>> According to the descriptionof PWM for pwmcmp in SiFive FU740-C000 >>>>> Manual[1]. >>>>> The pwm algorithm is (PW) pulse active time = (D) duty * (T) >>>>> period[2]. >>>>> The `frac` variable is pulse "inactive" time so we need to invert it. >>>>> >>>>> So this patchset removes active-low in DTS and adds reverse logic to >>>>> the driver. >>>>> >>>>> [0]:https://sifive-china.oss-cn-zhangjiakou.aliyuncs.com/HiFIve%20Unmatched/hifive-unmatched-schematics-v3.pdf >>>>> >>>>> [1]:https://sifive-china.oss-cn-zhangjiakou.aliyuncs.com/HiFIve%20Unmatched/fu740-c000-manual-v1p2.pdf >>>>> >>>>> [2]:https://en.wikipedia.org/wiki/Duty_cycle >>>> Please delete link 2, convert the other two to standard Link: tags and >>>> put this information in the dts patch. Possibly into the PWM patch >>>> too, >>>> depending on what the PWM maintainers think. >> I got it. I will fix it. >>>> This info should be in the commit history IMO and the commit >>>> message for >>>> the dts patch says what's obvious from the diff without any >>>> explanation >>>> as to why. >>>> >>>> I did a bit of looking around on lore, to see if I could figure out >>>> why it was done like this in the first place, and I found: >>>> https://lore.kernel.org/linux-pwm/CAJ2_jOG2M03aLBgUOgGjWH9CUxq2aTG97eSX70=UaSbGCMMF_g@mail.gmail.com/ >>>> >>> That DTS documentation makes no sense to me, why does what the LED is >>> wired to matter? Whether you have your transistor next to ground or >>> next to Vdd doesn’t matter, what matters is whether the transistor is >>> on or off. Maybe what they mean is whether the *PWM's output* / *the >>> transistor's input* is pulled to ground or Vdd? In which case the >>> property would indeed not apply here. >>> >>> Unless that’s written assuming the LED is wired directly to the PWM, in >>> which case it would make sense, but that’s a very narrow-minded view of >>> what the PWM output is (directly) driving. >>> >>> Jess >>> >> This is a HiFive Unmatched/Unleashed LED-PWM layout >> >> VDD >> | >> | >> _____ >> \ / LED >> \ / >> --- >> | >> | >> | >> ______ >> | | >> - | >> ^ --> |------ PWM >> |___|___| >> | >> | >> __ >> - >> GND >> >> - the waveform >> e.g. duty=30s, period=100s, actvie-high = 30%, active-low = 70% >> >> V >> ^ >> | >> | ----------| >> | | >> | | >> |______ |__________ > t >> >> When VCC is high, the LED will be illuminated, which is an active-high >> logic. This is why we need to remove "active-low". >> >> So, according to my understanding, Unleashed's DTS should also remove >> active-low. >>>> That doesn't explain the driver, but it does explain the dts being >>>> that >>>> way. Perhaps a Fixes tag is also in order? But only if both patches >>>> get >>>> one, otherwise backporting would lead to breakage. >>>> >>>> The min() construct appears to have been there since the RFC driver >>>> was >>>> first posted. >>>> >>>> Thanks, >>>> Conor. >>>> >>>>> Nylon Chen (2): >>>>> riscv: dts: sifive unmatched: Remove PWM controlled LED's >>>>> active-low >>>> nit: s/sifive unmatched:/sifive: unmatched:/ >> I got it. I will fix it. >> >>>>> properties >>>>> pwm: sifive: change the PWM controlled LED algorithm >>>>> >>>>> arch/riscv/boot/dts/sifive/hifive-unmatched-a00.dts | 4 ---- >>>>> drivers/pwm/pwm-sifive.c | 1 + >>>>> 2 files changed, 1 insertion(+), 4 deletions(-) >>>>> >>>>> -- >>>>> 2.36.1 > > I've tested this patch. For some reason, the heartbeat function no > longer works for D12. This is my /etc/udev/rules.d/99-pwm-leds.rules > file contents: > > # D12 LED: heartbeat > SUBSYSTEM=="leds", KERNEL=="d12", ACTION=="add", > ATTR{trigger}="heartbeat" > > # D2 RGB LED: boot status > SUBSYSTEM=="leds", KERNEL=="d2", ACTION=="add", > ATTR{trigger}="default-on", ATTR{multi_intensity}="25 25 25" > > This is from https://github.com/sifive/meta-sifive, but modified for > the multi_intensity driver introduced in Linux 6.0. > I've instrumented this patch with some printks. The reason the heartbeat doesn't work is that setting the LEDs to maximum brightness causes the variable "frac" to be set to -1 instead of 0.
You can test it with:
# /bin/echo "255" > /sys/class/leds/d12/brightness
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