[PATCH 1/7] drm/omap: ensure all displays have been probed

[Tomi Valkeinen <tomi.valkeinen@xxxxxx>]

DRM offers no ways to add new displays after the DRM driver has been
loaded. This causes issues on boards that have multiple displays, and
omapdrm is loaded when some of them are loaded but not all. The result
is that omapdrm starts with the displays that were loaded at that time,
ignoring the displays loaded later.

This patch changes the behavior so that omapdrm ensures all display are
loaded which have an alias in the .dts file.

The downside is that this prevents omapdrm from loading if, say, the
user has not compiled a kernel module for one of the displays, or
there's some kind of failure in one of the displays. Thus, after this
patch, all the displays have to work, or none does.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@xxxxxx>
---
 drivers/gpu/drm/omapdrm/omap_drv.c | 27 +++++++++++++++++++++++++++
 1 file changed, 27 insertions(+)

diff --git a/drivers/gpu/drm/omapdrm/omap_drv.c b/drivers/gpu/drm/omapdrm/omap_drv.c
index 5c6609cbb6a2..c93c13e2c22d 100644
--- a/drivers/gpu/drm/omapdrm/omap_drv.c
+++ b/drivers/gpu/drm/omapdrm/omap_drv.c
@@ -242,11 +242,38 @@ static void omap_disconnect_dssdevs(void)
 		dssdev->driver->disconnect(dssdev);
 }
 
+static bool dssdev_with_alias_exists(const char *alias)
+{
+	struct omap_dss_device *dssdev = NULL;
+
+	for_each_dss_dev(dssdev) {
+		if (strcmp(alias, dssdev->alias) == 0) {
+			omap_dss_put_device(dssdev);
+			return true;
+		}
+	}
+
+	return false;
+}
+
 static int omap_connect_dssdevs(void)
 {
 	int r;
 	struct omap_dss_device *dssdev = NULL;
 	bool no_displays = true;
+	struct device_node *aliases;
+	struct property *pp;
+
+	aliases = of_find_node_by_path("/aliases");
+	if (aliases) {
+		for_each_property_of_node(aliases, pp) {
+			if (strncmp(pp->name, "display", 7) != 0)
+				continue;
+
+			if (dssdev_with_alias_exists(pp->name) == false)
+				return -EPROBE_DEFER;
+		}
+	}
 
 	for_each_dss_dev(dssdev) {
 		r = dssdev->driver->connect(dssdev);
-- 
2.5.0

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