[PATCH v2] dt-bindings: pwm: st,pwm: convert to DT schema

[PATCH v2] dt-bindings: pwm: st,pwm: convert to DT schema

[Charan Pedumuru]

Convert STMicroelectronics STiH41x PWM/Capture controller binding
to DT schema.
Changes during conversion:
- Add 'interrupts' to the required list. The text binding listed it
  as required and the driver unconditionally calls platform_get_irq().
- Drop pinctrl-0 from the required list as pinctrl properties are
  inherited and validated by the pinctrl schema.

Signed-off-by: Charan Pedumuru <charan.pedumuru@gmail.com>
---
Changes in v2:
- Add the missing interrupts to the required following the old binding.
- Modify commit message to explain the changes made.
- Link to v1: https://patch.msgid.link/20260613-st-pwm-v1-1-458c2c89709a@gmail.com
---
 Documentation/devicetree/bindings/pwm/pwm-st.txt  | 43 -----------
 Documentation/devicetree/bindings/pwm/st,pwm.yaml | 93 +++++++++++++++++++++++
 2 files changed, 93 insertions(+), 43 deletions(-)

diff --git a/Documentation/devicetree/bindings/pwm/pwm-st.txt b/Documentation/devicetree/bindings/pwm/pwm-st.txt
deleted file mode 100644
index 19fce774cafa..000000000000
--- a/Documentation/devicetree/bindings/pwm/pwm-st.txt
+++ /dev/null
@@ -1,43 +0,0 @@
-STMicroelectronics PWM driver bindings
---------------------------------------
-
-Required parameters:
-- compatible :		"st,pwm"
-- #pwm-cells : 		Number of cells used to specify a PWM. First cell
-			specifies the per-chip index of the PWM to use and the
-			second cell is the period in nanoseconds - fixed to 2
-			for STiH41x.
-- reg :			Physical base address and length of the controller's
-			registers.
-- pinctrl-names: 	Set to "default".
-- pinctrl-0: 		List of phandles pointing to pin configuration nodes
-			for PWM module.
-			For Pinctrl properties, please refer to [1].
-- clock-names: 		Valid entries are "pwm" and/or "capture".
-- clocks: 		phandle of the clock used by the PWM module.
-			For Clk properties, please refer to [2].
-- interrupts:		IRQ for the Capture device
-
-Optional properties:
-- st,pwm-num-chan:	Number of available PWM channels.  Default is 0.
-- st,capture-num-chan:	Number of available Capture channels.  Default is 0.
-
-[1] Documentation/devicetree/bindings/pinctrl/pinctrl-bindings.txt
-[2] Documentation/devicetree/bindings/clock/clock-bindings.txt
-
-Example:
-
-pwm1: pwm@fe510000 {
-	compatible = "st,pwm";
-	reg = <0xfe510000 0x68>;
-	#pwm-cells = <2>;
-	pinctrl-names = "default";
-	pinctrl-0 = <&pinctrl_pwm1_chan0_default
-		     &pinctrl_pwm1_chan1_default
-		     &pinctrl_pwm1_chan2_default
-		     &pinctrl_pwm1_chan3_default>;
-	clocks = <&clk_sysin>;
-	clock-names = "pwm";
-	st,pwm-num-chan = <4>;
-	st,capture-num-chan = <2>;
-};
diff --git a/Documentation/devicetree/bindings/pwm/st,pwm.yaml b/Documentation/devicetree/bindings/pwm/st,pwm.yaml
new file mode 100644
index 000000000000..a045502e0e70
--- /dev/null
+++ b/Documentation/devicetree/bindings/pwm/st,pwm.yaml
@@ -0,0 +1,93 @@
+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/pwm/st,pwm.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: STMicroelectronics STiH41x PWM/Capture controller
+
+maintainers:
+  - Ajit Pal Singh <ajitpal.singh@st.com>
+
+description:
+  The STiH41x PWM controller supports both PWM output and input capture
+  functionality. It provides multiple PWM output channels for generating
+  variable duty-cycle waveforms, and multiple input capture channels for
+  measuring external signal periods and pulse widths. PWM output channels
+  and input capture channels are configured independently via
+  st,pwm-num-chan and st,capture-num-chan respectively.
+
+allOf:
+  - $ref: pwm.yaml#
+
+properties:
+  compatible:
+    const: st,pwm
+
+  reg:
+    maxItems: 1
+
+  "#pwm-cells":
+    const: 2
+
+  pinctrl-names:
+    const: default
+
+  clock-names:
+    items:
+      enum: [pwm, capture]
+    minItems: 1
+    maxItems: 2
+
+  clocks:
+    minItems: 1
+    maxItems: 2
+
+  interrupts:
+    description: IRQ line for the capture device.
+    maxItems: 1
+
+  st,pwm-num-chan:
+    $ref: /schemas/types.yaml#/definitions/uint32
+    description: Number of available PWM output channels.
+    minimum: 0
+    maximum: 4
+    default: 0
+
+  st,capture-num-chan:
+    $ref: /schemas/types.yaml#/definitions/uint32
+    description: Number of available input capture channels.
+    minimum: 0
+    maximum: 4
+    default: 0
+
+required:
+  - reg
+  - compatible
+  - "#pwm-cells"
+  - pinctrl-names
+  - clock-names
+  - clocks
+  - interrupts
+
+unevaluatedProperties: false
+
+examples:
+  - |
+    #include <dt-bindings/interrupt-controller/arm-gic.h>
+    pwm@fe510000 {
+        compatible = "st,pwm";
+        reg = <0xfe510000 0x68>;
+        interrupts = <GIC_SPI 128 IRQ_TYPE_LEVEL_HIGH>;
+        #pwm-cells = <2>;
+        pinctrl-names = "default";
+        pinctrl-0 = <&pinctrl_pwm1_chan0_default
+                     &pinctrl_pwm1_chan1_default
+                     &pinctrl_pwm1_chan2_default
+                     &pinctrl_pwm1_chan3_default>;
+        clocks = <&clk_sysin>;
+        clock-names = "pwm";
+        st,pwm-num-chan = <4>;
+        st,capture-num-chan = <2>;
+    };
+...

---
base-commit: c425609d6ac4012c8bbf01ec2e10e801b1923a7b
change-id: 20260613-st-pwm-1feade6cfea3

Best regards,
--  
Charan Pedumuru <charan.pedumuru@gmail.com>

Re: [PATCH v2] dt-bindings: pwm: st,pwm: convert to DT schema

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 3 potential issue(s) to consider:

New issues:
- [High] The YAML binding strictly validates against `st,pwm`, but the hardware driver and actual device trees use `st,sti-pwm`.
- [Medium] The schema drops `pinctrl-0` from the required list but keeps `pinctrl-names` as required, creating an inconsistent configuration requirement.

Pre-existing issues:
- [High] The driver requests the IRQ before fully initializing the regmap fields used by the interrupt handler, creating a race condition that can lead to a NULL pointer dereference.
--

commit e38e89bd06d5e023d198bb6e9fb8add957cdf8e9
Author: Charan Pedumuru <charan.pedumuru@gmail.com>

dt-bindings: pwm: st,pwm: convert to DT schema

This commit converts the STMicroelectronics STiH41x PWM/Capture controller
text binding to DT schema. It updates the required list by adding
'interrupts' and dropping 'pinctrl-0'.

> diff --git a/Documentation/devicetree/bindings/pwm/st,pwm.yaml b/Documentation/devicetree/bindings/pwm/st,pwm.yaml
> new file mode 100644
> index 0000000000000..a045502e0e704
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/pwm/st,pwm.yaml
> @@ -0,0 +1,93 @@
[ ... ]
> +properties:
> +  compatible:
> +    const: st,pwm

[Severity: High]
Does this compatible string match the hardware driver and actual device trees?

If existing in-kernel device trees and the matching driver
(drivers/pwm/pwm-sti.c) use "st,sti-pwm" instead of "st,pwm", will
make dtbs_check silently skip validation for them?

[ ... ]
> +  st,capture-num-chan:
> +    $ref: /schemas/types.yaml#/definitions/uint32
> +    description: Number of available input capture channels.
> +    minimum: 0
> +    maximum: 4
> +    default: 0
> +
> +required:
> +  - reg
> +  - compatible
> +  - "#pwm-cells"
> +  - pinctrl-names

[Severity: Medium]
Since 'pinctrl-0' was dropped from the required list, should 'pinctrl-names'
also be removed?

Retaining 'pinctrl-names' in the required list while making 'pinctrl-0'
optional forces device trees that do not define any pinctrl configuration
to include a meaningless pinctrl-names = "default"; just to pass schema
validation.

> +  - clock-names
> +  - clocks
> +  - interrupts
[ ... ]
> +examples:
> +  - |
> +    #include <dt-bindings/interrupt-controller/arm-gic.h>
> +    pwm@fe510000 {
> +        compatible = "st,pwm";

[Severity: High]
Does this example propagate an incorrect compatible string?

If the hardware actually uses "st,sti-pwm", using "st,pwm" here might mislead
future device tree authors.

[ ... ]

[Severity: High]
This is a pre-existing issue, but can the interrupt fire before the regmap
fields are fully initialized?

Looking at drivers/pwm/pwm-sti.c:sti_pwm_probe(), the IRQ is requested early:

	ret = devm_request_irq(&pdev->dev, irq, sti_pwm_interrupt, 0, ...);

Later, the regmap fields crucial for the IRQ handler are initialized:

	ret = sti_pwm_probe_regmap(pc);

If a pending interrupt from the bootloader fires immediately after
devm_request_irq(), sti_pwm_interrupt() will execute and call
regmap_field_read(pc->pwm_cpt_int_stat, ...). Since pc->pwm_cpt_int_stat
is NULL before sti_pwm_probe_regmap() initializes it, would this cause a
kernel panic due to a NULL pointer dereference?

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260618-st-pwm-v2-1-c792d5795ce2@gmail.com?part=1