drm/tilcdc: Add blue-and-red-crossed devicetree property

Add "blue-and-red-wiring"-device tree property and update devicetree
binding document.

The red and blue components are reversed between 24 and 16 bit modes
on am335x LCDC output pins. To get 24 RGB format the red and blue
wires has to be crossed and this in turn causes 16 colors output to be
in BGR format. With straight wiring the 16 color is RGB and 24 bit is
BGR.

The new property describes whether the red and blue wires are crossed
or not. If the property is not present or its value is not recognized
the legacy mode is assumed. The legacy configuration supports RGB565,
RGB888 and XRGB8888 formats. However, depending on wiring, the red and
blue colors are swapped in either 16 or 24-bit color modes.

For more details see section 3.1.1 in AM335x Silicon Errata:
http://www.ti.com/general/docs/lit/getliterature.tsp?baseLiteratureNumber=sprz360

Signed-off-by: Jyri Sarha <jsarha@ti.com>
Reviewed-by: Tomi Valkeinen <tomi.valkeinen@ti.com>

1 files changed, 41 insertions, 0 deletions

diff --git a/drivers/gpu/drm/tilcdc/tilcdc_drv.c b/drivers/gpu/drm/tilcdc/tilcdc_drv.c
index 1f29a9314d11..f7c3ca858bb8 100644
--- a/drivers/gpu/drm/tilcdc/tilcdc_drv.c
+++ b/drivers/gpu/drm/tilcdc/tilcdc_drv.c
@@ -33,6 +33,20 @@
 
 static LIST_HEAD(module_list);
 
+static const u32 tilcdc_rev1_formats[] = { DRM_FORMAT_RGB565 };
+
+static const u32 tilcdc_straight_formats[] = { DRM_FORMAT_RGB565,
+                                               DRM_FORMAT_BGR888,
+                                               DRM_FORMAT_XBGR8888 };
+
+static const u32 tilcdc_crossed_formats[] = { DRM_FORMAT_BGR565,
+                                              DRM_FORMAT_RGB888,
+                                              DRM_FORMAT_XRGB8888 };
+
+static const u32 tilcdc_legacy_formats[] = { DRM_FORMAT_RGB565,
+                                             DRM_FORMAT_RGB888,
+                                             DRM_FORMAT_XRGB8888 };
+
 void tilcdc_module_init(struct tilcdc_module *mod, const char *name,
                 const struct tilcdc_module_ops *funcs)
 {
@@ -318,6 +332,33 @@ static int tilcdc_load(struct drm_device *dev, unsigned long flags)
 
         pm_runtime_put_sync(dev->dev);
 
+        if (priv->rev == 1) {
+                DBG("Revision 1 LCDC supports only RGB565 format");
+                priv->pixelformats = tilcdc_rev1_formats;
+                priv->num_pixelformats = ARRAY_SIZE(tilcdc_rev1_formats);
+        } else {
+                const char *str = "\0";
+
+                of_property_read_string(node, "blue-and-red-wiring", &str);
+                if (0 == strcmp(str, "crossed")) {
+                        DBG("Configured for crossed blue and red wires");
+                        priv->pixelformats = tilcdc_crossed_formats;
+                        priv->num_pixelformats =
+                                ARRAY_SIZE(tilcdc_crossed_formats);
+                } else if (0 == strcmp(str, "straight")) {
+                        DBG("Configured for straight blue and red wires");
+                        priv->pixelformats = tilcdc_straight_formats;
+                        priv->num_pixelformats =
+                                ARRAY_SIZE(tilcdc_straight_formats);
+                } else {
+                        DBG("Blue and red wiring '%s' unknown, use legacy mode",
+                            str);
+                        priv->pixelformats = tilcdc_legacy_formats;
+                        priv->num_pixelformats =
+                                ARRAY_SIZE(tilcdc_legacy_formats);
+                }
+        }
+
         ret = modeset_init(dev);
         if (ret < 0) {
                 dev_err(dev->dev, "failed to initialize mode setting\n");