linux-kernel - Re: [PATCH v6 3/8] drm: bridge: Cadence: Add MHDP8501 DP driver

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Date:   Thu, 15 Jun 2023 18:33:08 +0200
From:   Sam Ravnborg <sam@...nborg.org>
To:     Sandor Yu <Sandor.yu@....com>
Cc:     andrzej.hajda@...el.com, neil.armstrong@...aro.org,
        robert.foss@...aro.org, Laurent.pinchart@...asonboard.com,
        jonas@...boo.se, jernej.skrabec@...il.com, airlied@...il.com,
        daniel@...ll.ch, robh+dt@...nel.org,
        krzysztof.kozlowski+dt@...aro.org, shawnguo@...nel.org,
        s.hauer@...gutronix.de, festevam@...il.com, vkoul@...nel.org,
        dri-devel@...ts.freedesktop.org, devicetree@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-phy@...ts.infradead.org, oliver.brown@....com,
        linux-imx@....com, kernel@...gutronix.de
Subject: Re: [PATCH v6 3/8] drm: bridge: Cadence: Add MHDP8501 DP driver

Hi Sandor,

On Thu, Jun 15, 2023 at 09:38:13AM +0800, Sandor Yu wrote:
> Add a new DRM DisplayPort bridge driver for Candence MHDP8501
> used in i.MX8MQ SOC. MHDP8501 could support HDMI or DisplayPort
> standards according embedded Firmware running in the uCPU.
> 
> For iMX8MQ SOC, the DisplayPort FW was loaded and activated by SOC
> ROM code. Bootload binary included HDMI FW was required for the driver.

The bridge driver supports creating a connector, but is this really
necessary?

This part:
> +static const struct drm_connector_funcs cdns_dp_connector_funcs = {
> +	.fill_modes = drm_helper_probe_single_connector_modes,
> +	.destroy = drm_connector_cleanup,
> +	.reset = drm_atomic_helper_connector_reset,
> +	.atomic_duplicate_state = drm_atomic_helper_connector_duplicate_state,
> +	.atomic_destroy_state = drm_atomic_helper_connector_destroy_state,
> +};
> +
> +static const struct drm_connector_helper_funcs cdns_dp_connector_helper_funcs = {
> +	.get_modes = cdns_dp_connector_get_modes,
> +};
> +
> +static int cdns_dp_bridge_attach(struct drm_bridge *bridge,
> +				 enum drm_bridge_attach_flags flags)
> +{
> +	struct cdns_mhdp_device *mhdp = bridge->driver_private;
> +	struct drm_encoder *encoder = bridge->encoder;
> +	struct drm_connector *connector = &mhdp->connector;
> +	int ret;
> +
> +	if (!(flags & DRM_BRIDGE_ATTACH_NO_CONNECTOR)) {
> +		connector->interlace_allowed = 0;
> +
> +		connector->polled = DRM_CONNECTOR_POLL_HPD;
> +
> +		drm_connector_helper_add(connector, &cdns_dp_connector_helper_funcs);
> +
> +		drm_connector_init(bridge->dev, connector, &cdns_dp_connector_funcs,
> +				   DRM_MODE_CONNECTOR_DisplayPort);
> +
> +		drm_connector_attach_encoder(connector, encoder);
> +	}

Unless you have a display driver that do not create their own connector
then drop the above and error out if DRM_BRIDGE_ATTACH_NO_CONNECTOR is
not set.
It is encouraged that display drivers create their own connector.

This was the only detail I looked for in the driver, I hope some else
volunteer to review it.

	Sam