Re: [PATCH 0/2] Change PWM-controlled LED pin active mode and algorithm

[Ron Economos]

On 1/17/23 1:32 AM, Nylon Chen wrote:
> Hi Conor, Jessica
>
> thanks for your reply.
>
> Jessica Clarke <jrtc27@xxxxxxxxxx> 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@xxxxxxxxxx> 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@xxxxxxxxxxxxxx/
> > 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.