Re: [PATCH v15 0/7] Rust Abstractions for PWM subsystem with TH1520 PWM driver

Uwe Kleine-König
2025-10-13T16:48:38Z

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Hello,

my diff on top of your changes looks as follows:

diff --git a/drivers/pwm/Kconfig b/drivers/pwm/Kconfig
index dd6db01832ee..e7f770ecfe84 100644
--- a/drivers/pwm/Kconfig
+++ b/drivers/pwm/Kconfig
@@ -812,9 +812,8 @@ config PWM_XILINX
will be called pwm-xilinx.

config RUST_PWM_ABSTRACTIONS
- bool "Rust PWM abstractions support"
+ bool
depends on RUST
- depends on PWM=y
help
This option enables the safe Rust abstraction layer for the PWM
subsystem. It provides idiomatic wrappers and traits necessary for

i.e. make RUST_PWM_ABSTRACTIONS invisible, it is only supposed to be
selected and there is little (or even no?) use to enable it without a
selector.

diff --git a/drivers/pwm/pwm_th1520.rs b/drivers/pwm/pwm_th1520.rs
index c9fd1d8d17bc..a5666052b7ce 100644
--- a/drivers/pwm/pwm_th1520.rs
+++ b/drivers/pwm/pwm_th1520.rs
@@ -121,6 +121,7 @@ fn round_waveform_tohw(
wf: &pwm::Waveform,
) -> Result<pwm::RoundedWaveform<Self::WfHw>> {
let data = chip.drvdata();
+ let status = 0;

if wf.period_length_ns == 0 {
dev_dbg!(chip.device(), "Requested period is 0, disabling PWM.\n");
@@ -141,18 +142,13 @@ fn round_waveform_tohw(
if period_cycles == 0 {
dev_dbg!(
chip.device(),
- "Requested period {} ns is too small for clock rate {} Hz, disabling PWM.\n",
+ "Requested period {} ns is too small for clock rate {} Hz, rounding up.\n",
wf.period_length_ns,
rate_hz
);

- return Ok(pwm::RoundedWaveform {
- status: 0,
- hardware_waveform: Th1520WfHw {
- enabled: false,
- ..Default::default()
- },
- });
+ period_cycles = 1;
+ status = 1;
}

let mut duty_cycles = ns_to_cycles(wf.duty_length_ns, rate_hz).min(u64::from(u32::MAX));

i.e. round up for too small period requests ...

@@ -189,7 +185,7 @@ fn round_waveform_tohw(
);

Ok(pwm::RoundedWaveform {
- status: 0,
+ status: status,
hardware_waveform: wfhw,
})
}

... and return 1 then

@@ -355,7 +351,7 @@ fn probe(
"Clock rate {} Hz is too high, not supported.\n",
rate_hz
);
- return Err(ERANGE);
+ return Err(EINVAL);
}

let chip = pwm::Chip::new(

at least pwm-stm32 uses EINVAL. Having said that, I wonder if this check
is sensible here at all. pwm-stm32 does it to ensure that
mul_u64_u64_div_u64() does the right thing, but this exact issue doesn't
exist here.

Otherwise looks fine I think.

Best regards
Uwe

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