[PATCH v4 09/11] drm/bridge: imx8mp-hdmi-tx-connector-fixup: show a warning when adding the overlay

[Luca Ceresoli <luca.ceresoli@bootlin.com>]

Describing the HDMI connector in device tree is recommended. While the
overlay insertion is a workaround to avoid breaking existing devices, every
dts should be improved by adding a connector description.

Add a warning to make users aware as far as possible.

As a warning line cannot hold all the relevant info, add a detailed comment
in the code so it easy to find when the warning is seen.

Signed-off-by: Luca Ceresoli <luca.ceresoli@bootlin.com>
Reviewed-by: Liu Ying <victor.liu@nxp.com>

---

Changes in v4:
- add missing \n to warning string
- Add Liu's R-by

Patch added in v3. Kept as a separate comment w.r.t. the patch adding the
overlay to let it be added in a later moment in case we want to convert
existing dts files before adding the warning.
---
 .../gpu/drm/bridge/imx/imx8mp-hdmi-tx-connector-fixup.c | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/drivers/gpu/drm/bridge/imx/imx8mp-hdmi-tx-connector-fixup.c b/drivers/gpu/drm/bridge/imx/imx8mp-hdmi-tx-connector-fixup.c
index dc1736bfc3ac..aaac27d00590 100644
--- a/drivers/gpu/drm/bridge/imx/imx8mp-hdmi-tx-connector-fixup.c
+++ b/drivers/gpu/drm/bridge/imx/imx8mp-hdmi-tx-connector-fixup.c
@@ -44,6 +44,23 @@ static int __init imx8mp_hdmi_tx_connector_fixup_init(void)
 	if (endpoint)
 		return 0;
 
+	/*
+	 * Boards with an HDMI connector should describe it in a device
+	 * tree node with compatible = "hdmi-connector".
+	 *
+	 * If you see this warning, it means such a node was not found and
+	 * a fallback one is added using a device tree overlay. Please add
+	 * one in your device tree, also describing the exact connector
+	 * type (the added overlay assumes Type A as a fallback, but it
+	 * might be wrong).
+	 *
+	 * This node is necessary for modern DRM, where bridge drivers do
+	 * not create a connector (see the DRM_BRIDGE_ATTACH_NO_CONNECTOR
+	 * flag). See https://docs.kernel.org/gpu/drm-kms-helpers.html for
+	 * more info.
+	 */
+	pr_warn("Please add a hdmi-connector DT node for imx8mp-hdmi-tx.\n");
+
 	dtbo_start = __dtbo_imx8mp_hdmi_tx_connector_fixup_begin;
 	dtbo_size = __dtbo_imx8mp_hdmi_tx_connector_fixup_end -
 		    __dtbo_imx8mp_hdmi_tx_connector_fixup_begin;

-- 
2.53.0