[PATCH] drm/ast: Atomic CR/SR reg R/W

[KuoHsiang Chou]

1. Avoid IO-index racing
2. IO-index racing happened on resolustion switching
   and mouse moving at the same time
3. System hung while IO-index racing occurred.

Signed-off-by: KuoHsiang Chou <kuohsiang_c...@aspeedtech.com>
---
 drivers/gpu/drm/ast/ast_main.c | 48 +++++++++++++++++++++++++---------
 1 file changed, 36 insertions(+), 12 deletions(-)

diff --git a/drivers/gpu/drm/ast/ast_main.c b/drivers/gpu/drm/ast/ast_main.c
index 79a361867..1d8fa70c5 100644
--- a/drivers/gpu/drm/ast/ast_main.c
+++ b/drivers/gpu/drm/ast/ast_main.c
@@ -41,28 +41,52 @@ void ast_set_index_reg_mask(struct ast_private *ast,
                            uint32_t base, uint8_t index,
                            uint8_t mask, uint8_t val)
 {
-       u8 tmp;
-       ast_io_write8(ast, base, index);
-       tmp = (ast_io_read8(ast, base + 1) & mask) | val;
-       ast_set_index_reg(ast, base, index, tmp);
+       uint16_t volatile usData;
+       uint8_t  volatile jData;
+
+       do {
+               ast_io_write8(ast, base, index);
+               usData = ast_io_read16(ast, base);
+       } while ((uint8_t)(usData) != index);
+
+       jData  = (uint8_t)(usData >> 8);
+       jData &= mask;
+       jData |= val;
+       usData = ((uint16_t) jData << 8) | (uint16_t) index;
+       ast_io_write16(ast, base, usData);
 }

 uint8_t ast_get_index_reg(struct ast_private *ast,
                          uint32_t base, uint8_t index)
 {
-       uint8_t ret;
-       ast_io_write8(ast, base, index);
-       ret = ast_io_read8(ast, base + 1);
-       return ret;
+       uint16_t volatile usData;
+       uint8_t  volatile jData;
+
+       do {
+               ast_io_write8(ast, base, index);
+               usData = ast_io_read16(ast, base);
+       } while ((uint8_t)(usData) != index);
+
+       jData  = (uint8_t)(usData >> 8);
+
+       return jData;
 }

 uint8_t ast_get_index_reg_mask(struct ast_private *ast,
                               uint32_t base, uint8_t index, uint8_t mask)
 {
-       uint8_t ret;
-       ast_io_write8(ast, base, index);
-       ret = ast_io_read8(ast, base + 1) & mask;
-       return ret;
+       uint16_t volatile usData;
+       uint8_t  volatile jData;
+
+       do {
+               ast_io_write8(ast, base, index);
+               usData = ast_io_read16(ast, base);
+       } while ((uint8_t)(usData) != index);
+
+       jData  = (uint8_t)(usData >> 8);
+       jData &= mask;
+
+       return jData;
 }

 static void ast_detect_config_mode(struct drm_device *dev, u32 *scu_rev)
--
2.18.4