[[PATCH v2]] drm/ast: fixed reading monitor EDID not stable issue

[Y.C. Chen]

From: "Y.C. Chen" <yc_chen at aspeedtech.com>

v1: over-sample data to increase the stability with some specific monitors
v2: refine to avoid infinite loop

Signed-off-by: Y.C. Chen <yc_chen at aspeedtech.com>
---
 drivers/gpu/drm/ast/ast_mode.c | 34 ++++++++++++++++++++++++++++------
 1 file changed, 28 insertions(+), 6 deletions(-)

diff --git a/drivers/gpu/drm/ast/ast_mode.c b/drivers/gpu/drm/ast/ast_mode.c
index 5e77d45..092e9a7 100644
--- a/drivers/gpu/drm/ast/ast_mode.c
+++ b/drivers/gpu/drm/ast/ast_mode.c
@@ -972,9 +972,20 @@ 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;
+	volatile 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;
 }
 
@@ -982,9 +993,20 @@ 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;
+	volatile 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;
 }
 
@@ -997,7 +1019,7 @@ 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;
@@ -1013,7 +1035,7 @@ 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;
-- 
1.8.3.1