Re: [PATCH v5 3/6] pwm: Add rockchip PWMv4 driver

[Bas Vermeulen]

Hi Nicolas,

On Mon, Apr 20, 2026 at 06:52:40 PDT, Nicolas Frattaroli wrote:
> The Rockchip RK3576 brings with it a new PWM IP, in downstream code
> referred to as "v4". This new IP is different enough from the previous
> Rockchip IP that I felt it necessary to add a new driver for it, instead
> of shoehorning it in the old one.

The same IP block is in the RK3506 (Cortex-A7, arm32), where I am
carrying this series on top of 7.3. It works there, driving a PWM
backlight and a pwm-regulator for the core voltage, but two things in
this patch need adjusting for it to build on a 32-bit kernel and on
current mainline:

> +	if (rate) {
> +		wf->period_length_ns = DIV_ROUND_UP((u64)wfhw->period * NSEC_PER_SEC, rate);
> +		wf->duty_length_ns = DIV_ROUND_UP((u64)wfhw->duty * NSEC_PER_SEC, rate);
> +		wf->duty_offset_ns = DIV_ROUND_UP((u64)wfhw->offset * NSEC_PER_SEC, rate);

DIV_ROUND_UP() with a u64 numerator is a plain 64-bit division, which on
arm32 becomes a call to __aeabi_uldivmod that the kernel does not
provide:

  pwm-rockchip-v4.o: undefined reference to `__aeabi_uldivmod'

DIV_ROUND_UP_ULL() goes through div_u64() and works on both:

-		wf->period_length_ns = DIV_ROUND_UP((u64)wfhw->period * NSEC_PER_SEC, rate);
-		wf->duty_length_ns = DIV_ROUND_UP((u64)wfhw->duty * NSEC_PER_SEC, rate);
-		wf->duty_offset_ns = DIV_ROUND_UP((u64)wfhw->offset * NSEC_PER_SEC, rate);
+		wf->period_length_ns = DIV_ROUND_UP_ULL((u64)wfhw->period * NSEC_PER_SEC, rate);
+		wf->duty_length_ns = DIV_ROUND_UP_ULL((u64)wfhw->duty * NSEC_PER_SEC, rate);
+		wf->duty_offset_ns = DIV_ROUND_UP_ULL((u64)wfhw->offset * NSEC_PER_SEC, rate);

Since MFD_ROCKCHIP_MFPWM allows COMPILE_TEST this will also show up in
32-bit allmodconfig builds.

> +	/*
> +	 * For referencing the PWM in the DT to work, we need the parent MFD
> +	 * device's OF node.
> +	 */
> +	dev->of_node_reused = true;

struct device no longer has that member: since 7.2 the flag lives in
the device flag word (commit 4aca5e62f37d "driver core: Replace
dev->of_node_reused with dev_of_node_reused()"), so this does not compile
against current mainline. The accessor is:

-	dev->of_node_reused = true;
+	dev_set_of_node_reused(dev);

With those two changes the driver builds and runs on the RK3506 with
7.3.y; happy to add a Tested-by for that if useful.

Regards,
Bas