Re: [PATCH v12 1/3] dt-bindings: pwm: Add binding for Allwinner D1/T113-S3/R329 PWM controller

Hello Andre,

On Thu, Jun 19, 2025 at 01:10:44PM +0100, Andre Przywara wrote:

On Thu, 19 Jun 2025 11:44:07 +0200
Alexandre Belloni [off-list ref] wrote:

Hi Alexandre,

quoted

On 12/05/2025 23:56:19+0100, Andre Przywara wrote:

quoted

On Sun, 27 Apr 2025 17:24:53 +0300
Aleksandr Shubin [off-list ref] wrote:

Hi,
  

quoted

Allwinner's D1, T113-S3 and R329 SoCs have a new pwm
controller witch is different from the previous pwm-sun4i.

The D1 and T113 are identical in terms of peripherals,
they differ only in the architecture of the CPU core, and
even share the majority of their DT. Because of that,
using the same compatible makes sense.
The R329 is a different SoC though, and should have
a different compatible string added, especially as there
is a difference in the number of channels.

D1 and T113s SoCs have one PWM controller with 8 channels.
R329 SoC has two PWM controllers in both power domains, one of
them has 9 channels (CPUX one) and the other has 6 (CPUS one).

Add a device tree binding for them.

Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
Signed-off-by: Aleksandr Shubin <redacted>
---
 .../bindings/pwm/allwinner,sun20i-pwm.yaml    | 84 +++++++++++++++++++
 1 file changed, 84 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/pwm/allwinner,sun20i-pwm.yaml

diff --git a/Documentation/devicetree/bindings/pwm/allwinner,sun20i-pwm.yaml b/Documentation/devicetree/bindings/pwm/allwinner,sun20i-pwm.yaml
new file mode 100644
index 000000000000..4b25e94a8e46
--- /dev/null
+++ b/Documentation/devicetree/bindings/pwm/allwinner,sun20i-pwm.yaml

@@ -0,0 +1,84 @@
+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/pwm/allwinner,sun20i-pwm.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Allwinner D1, T113-S3 and R329 PWM
+
+maintainers:
+  - Aleksandr Shubin <privatesub2@gmail.com>
+  - Brandon Cheo Fusi <fusibrandon13@gmail.com>
+
+properties:
+  compatible:
+    oneOf:
+      - const: allwinner,sun20i-d1-pwm
+      - items:
+          - const: allwinner,sun50i-r329-pwm
+          - const: allwinner,sun20i-d1-pwm
+
+  reg:
+    maxItems: 1
+
+  "#pwm-cells":
+    const: 3
+
+  clocks:
+    items:
+      - description: Bus clock
+      - description: 24 MHz oscillator
+      - description: APB clock
+
+  clock-names:
+    items:
+      - const: bus
+      - const: hosc
+      - const: apb
+
+  resets:
+    maxItems: 1
+
+  allwinner,npwms:
+    $ref: /schemas/types.yaml#/definitions/uint32
+    description: The number of PWM channels configured for this instance
+    enum: [6, 8, 9]  

Do we really need to be so restrictive here? The IP has an
"architectural" limit of 16 channels (due to the MMIO register layout
and status/control bits usage in some registers), so can't we just leave
this value to be anything between 1 and 16 here? If people configure
this wrongly, it's their fault, I'd say? Without confining this further
based on the respective compatible strings this enum is less useful
anyway, I think. The Allwinner A523 uses the same IP, and supports all
16 channels, the V853 implements 12, that's what I quickly found
already, and there might be more examples in the future, so I'd rather
open this up.
  

Do we really need this property? I feel like the number of PWM channels should be
something the driver could infer from the compatible string as we are going to
have one compatible string per SoC anyway.

Well yes, this would work, but I feel like it creates unnecessary churn to
touch the driver every time some new SoC with the same IP pops up, and
where just the number of channels is different - see above for a list of
SoCs we already know about, and there are more in the pipe. It also means
stable kernels would already work.

Having a property that specifies the number of PWM outputs is fine for
me.

There is some prior art for that: mxs-pwm.yaml has fsl,pwm-number;
pwm-st.txt has st,pwm-num-chan with that semantic.

Given that this is a fundamental concept of a pwm chip, I'd say giving
that a generic name without vendor prefix is justified. I suggest to go
for

	npwms = <..>;

which matches ngpios that is specified for gpio chips.

Best regards
Uwe