pwm: Add Rust driver for T-HEAD TH1520 SoC

Introduce a PWM driver for the T-HEAD TH1520 SoC, written in Rust and
utilizing the safe PWM abstractions from the preceding commit.

The driver implements the pwm::PwmOps trait using the modern waveform
API (round_waveform_tohw, write_waveform, etc.) to support configuration
of period, duty cycle, and polarity for the TH1520's PWM channels.

Resource management is handled using idiomatic Rust patterns. The PWM
chip object is allocated via pwm::Chip::new and its registration with
the PWM core is managed by the pwm::Registration RAII guard. This
ensures pwmchip_remove is always called when the driver unbinds,
preventing resource leaks. Device managed resources are used for the
MMIO region, and the clock lifecycle is correctly managed in the
driver's private data Drop implementation.

The driver's core logic is written entirely in safe Rust, with no unsafe
blocks, except for the Send and Sync implementations for the driver
data, which are explained in the comments.

Reviewed-by: Elle Rhumsaa <elle@weathered-steel.dev>
Signed-off-by: Michal Wilczynski <m.wilczynski@samsung.com>
Link: https://patch.msgid.link/20251016-rust-next-pwm-working-fan-for-sending-v16-4-a5df2405d2bd@samsung.com
Signed-off-by: Uwe Kleine-König <ukleinek@kernel.org>

Author: Michal Wilczynski

MAINTAINERS

@@ -22189,6 +22189,7 @@ F:	drivers/pinctrl/pinctrl-th1520.c
 F:	drivers/pmdomain/thead/
 F:	drivers/power/reset/th1520-aon-reboot.c
 F:	drivers/power/sequencing/pwrseq-thead-gpu.c
+F:	drivers/pwm/pwm_th1520.rs
 F:	drivers/reset/reset-th1520.c
 F:	include/dt-bindings/clock/thead,th1520-clk-ap.h
 F:	include/dt-bindings/power/thead,th1520-power.h

drivers/pwm/Kconfig

@@ -748,6 +748,17 @@ config PWM_TEGRA
 	  To compile this driver as a module, choose M here: the module
 	  will be called pwm-tegra.
 
+config PWM_TH1520
+	tristate "TH1520 PWM support"
+	depends on RUST
+	select RUST_PWM_ABSTRACTIONS
+	help
+	  This option enables the driver for the PWM controller found on the
+	  T-HEAD TH1520 SoC.
+
+	  To compile this driver as a module, choose M here; the module
+	  will be called pwm-th1520. If you are unsure, say N.
+
 config PWM_TIECAP
 	tristate "ECAP PWM support"
 	depends on ARCH_OMAP2PLUS || ARCH_DAVINCI_DA8XX || ARCH_KEYSTONE || ARCH_K3 || COMPILE_TEST

drivers/pwm/Makefile

@@ -68,6 +68,7 @@ obj-$(CONFIG_PWM_STMPE)		+= pwm-stmpe.o
 obj-$(CONFIG_PWM_SUN4I)		+= pwm-sun4i.o
 obj-$(CONFIG_PWM_SUNPLUS)	+= pwm-sunplus.o
 obj-$(CONFIG_PWM_TEGRA)		+= pwm-tegra.o
+obj-$(CONFIG_PWM_TH1520)	+= pwm_th1520.o
 obj-$(CONFIG_PWM_TIECAP)	+= pwm-tiecap.o
 obj-$(CONFIG_PWM_TIEHRPWM)	+= pwm-tiehrpwm.o
 obj-$(CONFIG_PWM_TWL)		+= pwm-twl.o