drm/ast: fixed reading monitor EDID not stable issue

[ Upstream commit 300625620314194d9e6d4f6dda71f2dc9cf62d9f ]

v1: over-sample data to increase the stability with some specific monitors
v2: refine to avoid infinite loop
v3: remove un-necessary "volatile" declaration

[airlied: fix two checkpatch warnings]
Signed-off-by: NY.C. Chen <yc_chen@aspeedtech.com>
Signed-off-by: NDave Airlie <airlied@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/1542858988-1127-1-git-send-email-yc_chen@aspeedtech.comSigned-off-by: NSasha Levin <sashal@kernel.org>

drivers/gpu/drm/ast/ast_mode.c

@@ -973,9 +973,21 @@ static int get_clock(void *i2c_priv)
 {
 	struct ast_i2c_chan *i2c = i2c_priv;
 	struct ast_private *ast = i2c->dev->dev_private;
-	uint32_t val;
+	uint32_t val, val2, count, pass;
+
+	count = 0;
+	pass = 0;
+	val = (ast_get_index_reg_mask(ast, AST_IO_CRTC_PORT, 0xb7, 0x10) >> 4) & 0x01;
+	do {
+		val2 = (ast_get_index_reg_mask(ast, AST_IO_CRTC_PORT, 0xb7, 0x10) >> 4) & 0x01;
+		if (val == val2) {
+			pass++;
+		} else {
+			pass = 0;
+			val = (ast_get_index_reg_mask(ast, AST_IO_CRTC_PORT, 0xb7, 0x10) >> 4) & 0x01;
+		}
+	} while ((pass < 5) && (count++ < 0x10000));
 
-	val = ast_get_index_reg_mask(ast, AST_IO_CRTC_PORT, 0xb7, 0x10) >> 4;
 	return val & 1 ? 1 : 0;
 }
 
@@ -983,9 +995,21 @@ static int get_data(void *i2c_priv)
 {
 	struct ast_i2c_chan *i2c = i2c_priv;
 	struct ast_private *ast = i2c->dev->dev_private;
-	uint32_t val;
+	uint32_t val, val2, count, pass;
+
+	count = 0;
+	pass = 0;
+	val = (ast_get_index_reg_mask(ast, AST_IO_CRTC_PORT, 0xb7, 0x20) >> 5) & 0x01;
+	do {
+		val2 = (ast_get_index_reg_mask(ast, AST_IO_CRTC_PORT, 0xb7, 0x20) >> 5) & 0x01;
+		if (val == val2) {
+			pass++;
+		} else {
+			pass = 0;
+			val = (ast_get_index_reg_mask(ast, AST_IO_CRTC_PORT, 0xb7, 0x20) >> 5) & 0x01;
+		}
+	} while ((pass < 5) && (count++ < 0x10000));
 
-	val = ast_get_index_reg_mask(ast, AST_IO_CRTC_PORT, 0xb7, 0x20) >> 5;
 	return val & 1 ? 1 : 0;
 }
 
@@ -998,7 +1022,7 @@ static void set_clock(void *i2c_priv, int clock)
 
 	for (i = 0; i < 0x10000; i++) {
 		ujcrb7 = ((clock & 0x01) ? 0 : 1);
-		ast_set_index_reg_mask(ast, AST_IO_CRTC_PORT, 0xb7, 0xfe, ujcrb7);
+		ast_set_index_reg_mask(ast, AST_IO_CRTC_PORT, 0xb7, 0xf4, ujcrb7);
 		jtemp = ast_get_index_reg_mask(ast, AST_IO_CRTC_PORT, 0xb7, 0x01);
 		if (ujcrb7 == jtemp)
 			break;
@@ -1014,7 +1038,7 @@ static void set_data(void *i2c_priv, int data)
 
 	for (i = 0; i < 0x10000; i++) {
 		ujcrb7 = ((data & 0x01) ? 0 : 1) << 2;
-		ast_set_index_reg_mask(ast, AST_IO_CRTC_PORT, 0xb7, 0xfb, ujcrb7);
+		ast_set_index_reg_mask(ast, AST_IO_CRTC_PORT, 0xb7, 0xf1, ujcrb7);
 		jtemp = ast_get_index_reg_mask(ast, AST_IO_CRTC_PORT, 0xb7, 0x04);
 		if (ujcrb7 == jtemp)
 			break;