Re: [PATCH v12] drm/bridge: imx: Add i.MX93 parallel display format configuration support

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [High] Returning a fallback format for unsupported output formats breaks DRM bridge format negotiation.
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--- Patch [1]: [PATCH v12] drm/bridge: imx: Add i.MX93 parallel display format configuration support ---
commit 62def9c6e85686d63c6204b71b54383955f8f9d1
Author: Liu Ying <[email protected]>
drm/bridge: imx: Add i.MX93 parallel display format configuration support

This commit introduces a new DRM bridge driver to support parallel display
format configuration on the NXP i.MX93 and i.MX91 SoCs. It handles format
conversions for the MEDIAMIX BLK-CTRL DISPLAY_MUX register.

> diff --git a/drivers/gpu/drm/bridge/imx/imx93-pdfc.c b/drivers/gpu/drm/bridge/imx/imx93-pdfc.c
> new file mode 100644
> index 0000000000000..b084409d22ef2
> --- /dev/null
> +++ b/drivers/gpu/drm/bridge/imx/imx93-pdfc.c
[ ... ]
> +static u32 *
> +imx93_pdfc_bridge_atomic_get_input_bus_fmts(struct drm_bridge *bridge,
> +					    struct drm_bridge_state *bridge_state,
> +					    struct drm_crtc_state *crtc_state,
> +					    struct drm_connector_state *conn_state,
> +					    u32 output_fmt,
> +					    unsigned int *num_input_fmts)
> +{
> +	struct imx93_pdfc *pdfc = bridge_to_imx93_pdfc(bridge);
> +	u32 *input_fmts;
> +
> +	*num_input_fmts = 0;
> +
> +	input_fmts = kmalloc_obj(*input_fmts);
> +	if (!input_fmts)
> +		return NULL;
> +
> +	*num_input_fmts = 1;
> +
> +	if (!imx93_pdfc_bus_output_fmt_supported(output_fmt)) {
> +		dev_dbg(pdfc->dev, "No valid output bus-fmt detected, fallback to MEDIA_BUS_FMT_RGB888_1X24\n");
> +		input_fmts[0] = MEDIA_BUS_FMT_RGB888_1X24;
> +		return input_fmts;
> +	}

[Severity: High]
Does returning a fallback format here break DRM bridge format negotiation?

When the downstream bridge requests an unsupported output format first,
drm_atomic_bridge_chain_select_bus_fmts() queries atomic_get_input_bus_fmts()
to check if the format is supported. By returning MEDIA_BUS_FMT_RGB888_1X24
instead of 0 formats, this driver falsely claims it can support the requested
output_fmt.

The core then proceeds with the unsupported format, which is correctly
rejected by imx93_pdfc_bridge_atomic_check(), aborting the modeset with
-EINVAL instead of gracefully negotiating a fallback.

Should this instead set *num_input_fmts = 0, free the array, and return NULL
when the output format is unsupported?

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Sashiko AI review · https://sashiko.dev/#/patchset/20260722-v6-18-topic-imx93-parallel-display-v12-1-a59dbb4dbc13@nxp.com?part=1