linux-kernel - [PATCH v3] drm/ast: astdp: fix loop timeout check

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Message-ID: <1ba8da25-2d09-4924-a4ff-c0714bfbb192@stanley.mountain>
Date: Mon, 12 Aug 2024 11:29:38 +0300
From: Dan Carpenter <dan.carpenter@...aro.org>
To: Thomas Zimmermann <tzimmermann@...e.de>
Cc: Dave Airlie <airlied@...hat.com>, Jocelyn Falempe <jfalempe@...hat.com>,
	Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
	Maxime Ripard <mripard@...nel.org>,
	David Airlie <airlied@...il.com>, Daniel Vetter <daniel@...ll.ch>,
	dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
	kernel-janitors@...r.kernel.org
Subject: [PATCH v3] drm/ast: astdp: fix loop timeout check

This code has an issue because it loops until "i" is set to UINT_MAX but
the test for failure assumes that "i" is set to zero.  The result is that
it will only print an error message if we succeed on the very last try.
Reformat the loop to count forwards instead of backwards.

Fixes: 2281475168d2 ("drm/ast: astdp: Perform link training during atomic_enable")
Signed-off-by: Dan Carpenter <dan.carpenter@...aro.org>
---
v3: V2 had the same bug but just without the always true if (i) statement.
    Remove the final sleep.
v2: In V1, I introduced a bug where it would msleep(100) after failure
    and that is a pointless thing to do.  Also change the loop to a for loop.
---
 drivers/gpu/drm/ast/ast_dp.c | 15 ++++++++-------
 1 file changed, 8 insertions(+), 7 deletions(-)

diff --git a/drivers/gpu/drm/ast/ast_dp.c b/drivers/gpu/drm/ast/ast_dp.c
index 5d07678b502c..ca022c287785 100644
--- a/drivers/gpu/drm/ast/ast_dp.c
+++ b/drivers/gpu/drm/ast/ast_dp.c
@@ -146,18 +146,19 @@ void ast_dp_power_on_off(struct drm_device *dev, bool on)
 void ast_dp_link_training(struct ast_device *ast)
 {
 	struct drm_device *dev = &ast->base;
-	unsigned int i = 10;
+	int i;
 
-	while (i--) {
-		u8 vgacrdc = ast_get_index_reg(ast, AST_IO_VGACRI, 0xdc);
+	for (i = 0; i < 10; i++) {
+		u8 vgacrdc;
 
-		if (vgacrdc & AST_IO_VGACRDC_LINK_SUCCESS)
-			break;
 		if (i)
 			msleep(100);
+
+		vgacrdc = ast_get_index_reg(ast, AST_IO_VGACRI, 0xdc);
+		if (vgacrdc & AST_IO_VGACRDC_LINK_SUCCESS)
+			return;
 	}
-	if (!i)
-		drm_err(dev, "Link training failed\n");
+	drm_err(dev, "Link training failed\n");
 }
 
 void ast_dp_set_on_off(struct drm_device *dev, bool on)
-- 
2.43.0