Re: [PATCH 2/4] ARM: dts: imx: add ti,deskew = <0> for ti,tfp410

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] Hardcoding incorrect hardware description based on a software driver bug
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commit e68637a2ada078494e7ee776597edfdccd03a72c
Author: Frank Li <Frank.Li@nxp.com>

ARM: dts: imx: add ti,deskew = <0> for ti,tfp410

This commit adds the required ti,deskew property to ti,tfp410 nodes
to fix dt_binding_check warnings. The value 0 is chosen based on the
default value found in the driver.

>     Add required proprety ti,deskew for ti,tfp410, which have not defined

This isn't a bug, but there's a typo (proprety) in the commit message.

>     default value in yaml. 0 is default value according to
>     drivers/gpu/drm/bridge/ti-tfp410.c.

Does this accurately describe the hardware, or is it mirroring a driver
bug?

Device Tree properties are intended to describe the physical hardware
configuration, rather than reflecting software driver fallbacks.

> diff --git a/arch/arm/boot/dts/nxp/imx/imx51-babbage.dts b/arch/arm/boot/dts/nxp/imx/imx51-babbage.dts
> index b17264e06e691..a02e9cd0b3fa0 100644
> --- a/arch/arm/boot/dts/nxp/imx/imx51-babbage.dts
> +++ b/arch/arm/boot/dts/nxp/imx/imx51-babbage.dts
> @@ -126,6 +126,7 @@ dvi_connector_in: endpoint {
>  
>  	dvi-encoder {
>  		compatible = "ti,tfp410";
> +		ti,deskew = <0>;

The driver fallback of 0 appears to be a bug introduced in 2020 by commit
"drm/bridge: tfp410: fix de-skew value retrieval from DT". That commit
changed the ti,deskew scale from -4..3 to 0..7 but did not update the
fallback value from 0 to 4.

As a result, missing properties inadvertently apply maximum negative skew
instead of neutral skew.

By copying this fallback into the device trees, does this permanently
enshrine maximum negative skew into the hardware description? 

If the driver is later fixed to use the correct neutral default, these
boards will still apply maximum negative skew.

Should the physical board schematics be consulted to determine the actual
DK[3:1] pin strapping instead? If the pins are strapped for neutral skew,
the value should likely be <4>.

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Sashiko AI review · https://sashiko.dev/#/patchset/20260511-b4-imx25_dts_simple_warning-v1-0-01b855a5ce25@nxp.com?part=2