linux-kernel - [PATCH v5 3/3] drm/panel-simple: allow LVDS format override

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Date:   Fri, 29 Sep 2023 14:33:33 +0200
From:   Johannes Zink <j.zink@...gutronix.de>
To:     David Airlie <airlied@...il.com>, Daniel Vetter <daniel@...ll.ch>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Thierry Reding <thierry.reding@...il.com>,
        Neil Armstrong <neil.armstrong@...aro.org>,
        Sam Ravnborg <sam@...nborg.org>
Cc:     kernel test robot <lkp@...el.com>,
        Dan Carpenter <error27@...il.com>,
        patchwork-jzi@...gutronix.de, kernel@...gutronix.de,
        Laurent Pinchart <laurent.pinchart+renesas@...asonboard.com>,
        dri-devel@...ts.freedesktop.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, Johannes Zink <j.zink@...gutronix.de>
Subject: [PATCH v5 3/3] drm/panel-simple: allow LVDS format override

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@...gutronix.de>

---

Changes:

  v4 -> v5: none

  v3 -> v4: - worked in Dan's feedback (thanks for reviewing my work):
                - return with a proper error in case the call to
		  panel_simple_override_nondefault_lvds_datamapping()
		  fails
                - drop the unneeded and ambiguous ret variable

  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@...el.com>
              Reported-by: Dan Carpenter <error27@...il.com>
              Link: https://lore.kernel.org/r/202304160359.4LHmFOlU-lkp@intel.com/
---
 drivers/gpu/drm/panel/panel-simple.c | 53 ++++++++++++++++++++++++++++++++++++
 1 file changed, 53 insertions(+)

diff --git a/drivers/gpu/drm/panel/panel-simple.c b/drivers/gpu/drm/panel/panel-simple.c
index 857bc01591db..4195cf54934b 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;
@@ -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 */
+		err = panel_simple_override_nondefault_lvds_datamapping(dev, panel);
+		if (err)
+			goto free_ddc;
+	}
+
 	connector_type = desc->connector_type;
 	/* Catch common mistakes for panels. */
 	switch (connector_type) {

-- 
2.39.2