Re: [PATCH v8 09/39] drm/display: hdmi-state-helper: Add fallback TMDS rate validation

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] The fallback TMDS character rate validation is silently bypassed for HDMI bridge connectors because the bridge framework unconditionally provides a wrapper callback.
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commit 98644f49de11eb659578421bd532a4a887719f94
Author: Cristian Ciocaltea <cristian.ciocaltea@collabora.com>

drm/display: hdmi-state-helper: Add fallback TMDS rate validation

Validate the computed TMDS character rate against connector limits when no
driver-specific hook is provided.

> diff --git a/drivers/gpu/drm/display/drm_hdmi_state_helper.c b/drivers/gpu/drm/display/drm_hdmi_state_helper.c
> index ce17eeefc2da4..db76699093e87 100644
> --- a/drivers/gpu/drm/display/drm_hdmi_state_helper.c
> +++ b/drivers/gpu/drm/display/drm_hdmi_state_helper.c
> @@ -566,6 +566,9 @@ hdmi_clock_valid(const struct drm_connector *connector,
>  		status = funcs->tmds_char_rate_valid(connector, mode, clock);
>  		if (status != MODE_OK)
>  			return status;
> +	} else if (connector->hdmi.max_tmds_char_rate) {

[Severity: Medium]
Does this else if structure bypass the fallback logic for HDMI bridge
connectors?

The bridge framework always provides a wrapper for its connectors:

drm_bridge_connector_tmds_char_rate_valid() {
        if (bridge->funcs->hdmi_tmds_char_rate_valid)
                return bridge->funcs->hdmi_tmds_char_rate_valid(...);
        else
                return MODE_OK;
}

Because this wrapper unconditionally exists, funcs->tmds_char_rate_valid
evaluates to true in hdmi_clock_valid().

If the underlying bridge lacks its own validation, the wrapper simply returns
MODE_OK. Since this was checked in the first if statement, the execution skips
the else if branch entirely.

Will this prevent the max_tmds_char_rate limit from being enforced on bridge
drivers, potentially allowing unsupported display modes to be selected?

> +		if (clock > connector->hdmi.max_tmds_char_rate)
> +			return MODE_CLOCK_HIGH;
>  	}
>  
>  	return MODE_OK;

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Sashiko AI review · https://sashiko.dev/#/patchset/20260702-dw-hdmi-qp-scramb-v8-0-d79890d00b6a@collabora.com?part=9