pinctrl: stm32: Introduce HDP driver

This patch introduce the driver for the Hardware Debug Port available on
STM32MP platforms. The HDP allows the observation of internal SoC
signals by using multiplexers. Each HDP port can provide up to 16
internal signals (one of them can be software controlled as a GPO).

Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Clément Le Goffic <clement.legoffic@foss.st.com>
Link: https://lore.kernel.org/20250711-hdp-upstream-v7-2-faeecf7aaee1@foss.st.com
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

Author: clegoffic

drivers/pinctrl/stm32/Kconfig

@@ -57,4 +57,18 @@ config PINCTRL_STM32MP257
 	depends on OF && HAS_IOMEM
 	default MACH_STM32MP25 || (ARCH_STM32 && ARM64)
 	select PINCTRL_STM32
+
+config PINCTRL_STM32_HDP
+	tristate "STMicroelectronics STM32 Hardware Debug Port (HDP) pin control"
+	depends on OF && HAS_IOMEM
+	default ARCH_STM32 && !ARM_SINGLE_ARMV7M
+	select PINMUX
+	select GENERIC_PINCONF
+	select GPIOLIB
+	help
+	  The Hardware Debug Port allows the observation of internal signals.
+	  It uses configurable multiplexer to route signals in a dedicated observation register.
+	  This driver also permits the observation of signals on external SoC pins.
+	  It permits the observation of up to 16 signals per HDP line.
+
 endif

drivers/pinctrl/stm32/Makefile

@@ -11,3 +11,4 @@ obj-$(CONFIG_PINCTRL_STM32H743)	+= pinctrl-stm32h743.o
 obj-$(CONFIG_PINCTRL_STM32MP135) += pinctrl-stm32mp135.o
 obj-$(CONFIG_PINCTRL_STM32MP157) += pinctrl-stm32mp157.o
 obj-$(CONFIG_PINCTRL_STM32MP257) += pinctrl-stm32mp257.o
+obj-$(CONFIG_PINCTRL_STM32_HDP) += pinctrl-stm32-hdp.o