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

[Liu Ying <victor.liu@nxp.com>]

On Wed, Jul 22, 2026 at 08:23:59AM +0000, sashiko-bot@kernel.org wrote:
> 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.
> --
> 
> --- Patch [1]: [PATCH v12] drm/bridge: imx: Add i.MX93 parallel display format configuration support ---
> commit 62def9c6e85686d63c6204b71b54383955f8f9d1
> Author: Liu Ying <victor.liu@nxp.com>
> 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.

Makes sense.  The reported issue was introduced by v8.  My earlier v5 does
the negotiation correctly.

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

No need to free any array.  Just need to set *num_input_fmts = 0 and then
return NULL when the output format is unsupported.

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

-- 
Regards,
Liu Ying