Re: [PATCH v6 08/17] dt-bindings: nvmem: microchip,sama7g5-otpc: add sama7d65 and dt node example

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 2 potential issue(s) to consider:
- [Medium] The device tree example for `sama7d65-otpc` incorrectly uses an ASCII string packet payload TAG ('ACST' / `0x41435354`) as an NVMEM cell `reg` offset, which breaks the driver's read implementation and nvmem API contract.
- [Medium] The calibration scale for `sama7d65_temp_calib` divides the baseline temperature by 1000, which contradicts the millicelsius requirement of the temperature sensor formula unless the hardware stores the value in microcelsius.
--

--- Patch [8]: [PATCH v6 08/17] dt-bindings: nvmem: microchip,sama7g5-otpc: add sama7d65 and dt node example ---
commit e1cdb410e4aef6d0fe6053ee57168bb1e5b19ab3
Author: Varshini Rajendran <varshini.rajendran@microchip.com>

dt-bindings: nvmem: microchip,sama7g5-otpc: add sama7d65 and dt node example

This commit adds support for the sama7d65 compatible string to the
microchip,sama7g5-otpc nvmem binding. It also includes a new device tree node
example demonstrating how a tag can be used to reference a packet stored in
the OTP memory.

> diff --git a/Documentation/devicetree/bindings/nvmem/microchip,sama7g5-otpc.yaml b/Documentation/devicetree/bindings/nvmem/microchip,sama7g5-otpc.yaml
> index cc25f2927682e..04b44660554ea 100644
> --- a/Documentation/devicetree/bindings/nvmem/microchip,sama7g5-otpc.yaml
> +++ b/Documentation/devicetree/bindings/nvmem/microchip,sama7g5-otpc.yaml

[ ... ]

> @@ -48,4 +54,20 @@ examples:
>          };
>      };
>  
> +  - |
> +    efuse@e8c00000 {
> +        compatible = "microchip,sama7d65-otpc", "microchip,sama7g5-otpc", "syscon";
> +        reg = <0xe8c00000 0x100>;
> +
> +        nvmem-layout {
> +            compatible = "fixed-layout";
> +            #address-cells = <1>;
> +            #size-cells = <1>;
> +
> +            calib@41435354 {
> +                reg = <0x41435354 0x2c>;    /* Temp calib data packet TAG */

[Severity: Medium]
Will using this packet tag as the reg offset cause a read failure at runtime?

Looking at mchp_otpc_read() in drivers/nvmem/microchip-otpc.c, the driver
expects the offset to be the sequential packet ID multiplied by 4:

	packet = mchp_otpc_id_to_packet(otpc, off / 4);
	if (!packet)
		return -EINVAL;

If the ASCII string 'ACST' (0x41435354) is provided as the physical memory
offset, won't this systematically fail during nvmem cell reads and return
-EINVAL?


[Severity: Medium]
Does the calibration scale for sama7d65_temp_calib in the ADC driver
incorrectly calculate the temperature?

In drivers/iio/adc/at91-sama5d2_adc.c, p1_scale is defined as:

	.p1_scale = { .numerator = 1, .denominator = 1000 },

When the scale ratio is applied in at91_adc_temp_sensor_init():

	clb->p1 *= layout->p1_scale.numerator;
	clb->p1 /= layout->p1_scale.denominator;

Dividing the baseline temperature by 1000 contradicts the millicelsius
requirement of the temperature sensor formula. Unless the hardware stores the
value natively in microcelsius, won't this round down or erroneously convert
the value to Celsius, corrupting the baseline temperature?

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260806074024.531259-1-varshini.rajendran@microchip.com?part=8