backlight: Factor known names into preferred interfaces

Since the /sys/device/backlight never turned up we face an issue with
disambiguating the backlight on multi-GPU devices. Both intel_backlight
and nv_backlight are presented are raw interfaces, and on modern systems
the ACPI interface is defunct, so we need a way to distinguish them. So,
we fallback to our priority table of known interfaces and rank them
accordingly, first by class (platform, native, raw) and then by priority.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>

1 files changed, 34 insertions, 26 deletions

diff --git a/src/backlight.c b/src/backlight.c
index c65e466b..d020a7c4 100644
--- a/src/backlight.c
+++ b/src/backlight.c
@@ -152,12 +152,9 @@ int backlight_open(struct backlight *b, char *iface)
 	return param.curval;
 }
 
-enum backlight_type backlight_exists(const char *iface)
+int backlight_exists(const char *iface)
 {
-	if (iface != NULL)
-		return BL_NONE;
-
-	return BL_PLATFORM;
+	return iface == NULL;
 }
 
 int backlight_on(struct backlight *b)
@@ -250,10 +247,10 @@ static const char *known_interfaces[] = {
 	"intel_backlight",
 };
 
-static enum backlight_type __backlight_type(const char *iface)
+static int __backlight_type(const char *iface)
 {
 	char buf[1024];
-	int fd, v;
+	int fd, v, i;
 
 	v = -1;
 	fd = __backlight_open(iface, "type", O_RDONLY);
@@ -267,39 +264,41 @@ static enum backlight_type __backlight_type(const char *iface)
 		buf[v] = '\0';
 
 		if (strcmp(buf, "raw") == 0)
-			v = BL_RAW;
+			v = BL_RAW << 8;
 		else if (strcmp(buf, "platform") == 0)
-			v = BL_PLATFORM;
+			v = BL_PLATFORM << 8;
 		else if (strcmp(buf, "firmware") == 0)
-			v = BL_FIRMWARE;
+			v = BL_FIRMWARE << 8;
 		else
-			v = BL_NAMED;
+			v = BL_NAMED << 8;
 	} else
-		v = BL_NAMED;
+		v = BL_NAMED << 8;
 
-	if (v == BL_NAMED) {
-		int i;
-		for (i = 0; i < ARRAY_SIZE(known_interfaces); i++) {
-			if (strcmp(iface, known_interfaces[i]) == 0)
-				break;
-		}
-		v += i;
+	for (i = 0; i < ARRAY_SIZE(known_interfaces); i++) {
+		if (strcmp(iface, known_interfaces[i]) == 0)
+			break;
 	}
+	v += i;
 
 	return v;
 }
 
-enum backlight_type backlight_exists(const char *iface)
+static int __backlight_exists(const char *iface)
 {
 	if (__backlight_read(iface, "brightness") < 0)
-		return BL_NONE;
+		return -1;
 
 	if (__backlight_read(iface, "max_brightness") <= 0)
-		return BL_NONE;
+		return -1;
 
 	return __backlight_type(iface);
 }
 
+int backlight_exists(const char *iface)
+{
+	return __backlight_exists(iface) != -1;
+}
+
 static int __backlight_init(struct backlight *b, char *iface, int fd)
 {
 	b->fd = fd_move_cloexec(fd_set_nonblock(fd));
@@ -405,7 +404,10 @@ __backlight_find(void)
 			continue;
 
 		/* Fallback to priority list of known iface for old kernels */
-		v = backlight_exists(de->d_name);
+		v = __backlight_exists(de->d_name);
+		if (v < 0)
+			continue;
+
 		if (v < best_type) {
 			char *copy = strdup(de->d_name);
 			if (copy) {
@@ -422,14 +424,17 @@ __backlight_find(void)
 
 int backlight_open(struct backlight *b, char *iface)
 {
-	int level;
+	int level, type;
 
 	if (iface == NULL)
 		iface = __backlight_find();
 	if (iface == NULL)
 		goto err;
 
-	b->type = __backlight_type(iface);
+	type = __backlight_type(iface);
+	if (type < 0)
+		goto err;
+	b->type = type >> 8;
 
 	b->max = __backlight_read(iface, "max_brightness");
 	if (b->max <= 0)
@@ -549,7 +554,10 @@ char *backlight_find_for_device(struct pci_device *pci)
 		if (*de->d_name == '.')
 			continue;
 
-		v = backlight_exists(de->d_name);
+		v = __backlight_exists(de->d_name);
+		if (v < 0)
+			continue;
+
 		if (v < best_type) {
 			char *copy = strdup(de->d_name);
 			if (copy) {