[PATCH v3 3/3] drm/panel-simple: allow LVDS format override

[Johannes Zink]

Some panels support multiple LVDS data mapping formats, which can be
used e.g. run displays on jeida-18 format when only 3 LVDS lanes are
available.

Add parsing of an optional data-mapping devicetree property, which also
touches up the bits per color to match the bus format.

Signed-off-by: Johannes Zink <j.zink at pengutronix.de>

---

Changes:

  v2 -> v3: - worked in Laurent's review findings (thanks for reviewing
              my work):
	        - extract fixing up the bus format to separate
		  function
		- only call function on LVDS panels
		- fix typos found by Laurent
		- simplified error handling

  v1 -> v2: - fix missing unwind goto found by test robot
              Reported-by: kernel test robot <lkp at intel.com>
              Reported-by: Dan Carpenter <error27 at gmail.com>
              Link: https://lore.kernel.org/r/202304160359.4LHmFOlU-lkp@intel.com/
---
 drivers/gpu/drm/panel/panel-simple.c | 55 +++++++++++++++++++++++++++++++++++-
 1 file changed, 54 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/panel/panel-simple.c b/drivers/gpu/drm/panel/panel-simple.c
index 4badda6570d5..0c25718dcb56 100644
--- a/drivers/gpu/drm/panel/panel-simple.c
+++ b/drivers/gpu/drm/panel/panel-simple.c
@@ -40,6 +40,7 @@
 #include <drm/drm_edid.h>
 #include <drm/drm_mipi_dsi.h>
 #include <drm/drm_panel.h>
+#include <drm/drm_of.h>
 
 /**
  * struct panel_desc - Describes a simple panel.
@@ -549,6 +550,51 @@ static void panel_simple_parse_panel_timing_node(struct device *dev,
 		dev_err(dev, "Reject override mode: No display_timing found\n");
 }
 
+static int panel_simple_override_nondefault_lvds_datamapping(struct device *dev,
+							     struct panel_simple *panel)
+{
+	int ret, bpc;
+
+	ret = drm_of_lvds_get_data_mapping(dev->of_node);
+	if (ret < 0) {
+		if (ret == -EINVAL)
+			dev_warn(dev, "Ignore invalid data-mapping property\n");
+
+		/*
+		 * Ignore non-existing or malformatted property, fallback to
+		 * default data-mapping, and return 0.
+		 */
+		return 0;
+	}
+
+	switch (ret) {
+	default:
+		WARN_ON(1);
+		fallthrough;
+	case MEDIA_BUS_FMT_RGB888_1X7X4_SPWG:
+		fallthrough;
+	case MEDIA_BUS_FMT_RGB888_1X7X4_JEIDA:
+		bpc = 8;
+		break;
+	case MEDIA_BUS_FMT_RGB666_1X7X3_SPWG:
+		bpc = 6;
+	}
+
+	if (panel->desc->bpc != bpc || panel->desc->bus_format != ret) {
+		struct panel_desc *override_desc;
+
+		override_desc = devm_kmemdup(dev, panel->desc, sizeof(*panel->desc), GFP_KERNEL);
+		if (!override_desc)
+			return -ENOMEM;
+
+		override_desc->bus_format = ret;
+		override_desc->bpc = bpc;
+		panel->desc = override_desc;
+	}
+
+	return 0;
+}
+
 static int panel_simple_probe(struct device *dev, const struct panel_desc *desc)
 {
 	struct panel_simple *panel;
@@ -556,7 +602,7 @@ static int panel_simple_probe(struct device *dev, const struct panel_desc *desc)
 	struct device_node *ddc;
 	int connector_type;
 	u32 bus_flags;
-	int err;
+	int err, ret;
 
 	panel = devm_kzalloc(dev, sizeof(*panel), GFP_KERNEL);
 	if (!panel)
@@ -601,6 +647,13 @@ static int panel_simple_probe(struct device *dev, const struct panel_desc *desc)
 			panel_simple_parse_panel_timing_node(dev, panel, &dt);
 	}
 
+	if (desc->connector_type == DRM_MODE_CONNECTOR_LVDS) {
+		/* Optional data-mapping property for overriding bus format */
+		ret = panel_simple_override_nondefault_lvds_datamapping(dev, panel);
+		if (ret)
+			goto free_ddc;
+	}
+
 	connector_type = desc->connector_type;
 	/* Catch common mistakes for panels. */
 	switch (connector_type) {

-- 
2.39.2