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

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Date:   Fri, 17 Sep 2021 15:22:26 +0800
From:   KuoHsiang Chou <kuohsiang_chou@...eedtech.com>
To:     <tzimmermann@...e.de>, <dri-devel@...ts.freedesktop.org>,
        <linux-kernel@...r.kernel.org>
CC:     <airlied@...hat.com>, <airlied@...ux.ie>, <daniel@...ll.ch>,
        <jenmin_yuan@...eedtech.com>, <kuohsiang_chou@...eedtech.com>,
        <arc_sung@...eedtech.com>
Subject: [PATCH] drm/ast: Atomic CR/SR reg R/W

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_chou@...eedtech.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