drm/ast: Linux 4.14 AST DRM driver might not load gamma table [patch proposed]

* drm/ast: Linux 4.14 AST DRM driver might not load gamma table [patch proposed]
@ 2017-12-18  0:08 Carroll, Lewis
  2017-12-20 23:29 ` Harry Wentland
  0 siblings, 1 reply; 8+ messages in thread
From: Carroll, Lewis @ 2017-12-18  0:08 UTC (permalink / raw)
  To: dri-devel


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Happy Holidays.

Test-driving Linux 4.14 from the Ubuntu Bionic repo on an AMD EPYC server using the A-Speed AST2500 BMC and the AST DRM driver and framebuffer console configured into the kernel, I have observed multiple systems where the analog VGA color palette for the framebuffer console is incorrect. Background is blue and all text colors other than white / gray are incorrect.

Instrumenting the AST DRM driver, it seems the default gamma table isn't loaded to the silicon until there is a DPMS action. When there is a DPMS action other than DPMS OFF, the gamma table is loaded and all is well. On these boards, the kernel is not calling for a DPMS event at driver init so the gamma table is not loaded.

The attached proposed patch adds a DPMS ON event to the commit callback after a kernel modeset call. This solves the problem, however there may be a better / more proper way to solve this.

Assuming no one on the mailing list has hardware on which to verify this, I am happy to be a test driver for any suggested fixes.

Regards,

Lewis Carroll
Principal Solutions Architect
AMD Enterprise Business Group


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From 0a0649f37c5015c0d60aef08e1ac9d496120d8a3 Mon Sep 17 00:00:00 2001
From: Lewis Carroll <lewis.carroll@amd.com>
Date: Sat, 16 Dec 2017 23:47:13 -0500
Subject: [PATCH] drm/ast: Fix corrupted gamma when DPMS enable is not needed
 at driver init

Under a scenario where a connector is already active at driver init, the
driver will not make a DPMS ON call, thus the gamma table is not loaded to
the silicon. This can result in corrupted colors on the display. Add a DPMS
ON call in the commit callback to force this to happen.

Move hard-coded gamma table size to a macro

Non-functional whitespace clean-up
---
 drivers/gpu/drm/ast/ast_mode.c   | 13 +++++--------
 drivers/gpu/drm/ast/ast_tables.h |  2 ++
 2 files changed, 7 insertions(+), 8 deletions(-)

diff --git a/drivers/gpu/drm/ast/ast_mode.c b/drivers/gpu/drm/ast/ast_mode.c
index 6f3849e..064c619 100644
--- a/drivers/gpu/drm/ast/ast_mode.c
+++ b/drivers/gpu/drm/ast/ast_mode.c
@@ -73,7 +73,7 @@ static void ast_crtc_load_lut(struct drm_crtc *crtc)
 	g = r + crtc->gamma_size;
 	b = g + crtc->gamma_size;
 
-	for (i = 0; i < 256; i++)
+	for (i = 0; i < AST_GAMMA_LUT_SIZE; i++)
 		ast_load_palette_index(ast, i, *r++ >> 8, *g++ >> 8, *b++ >> 8);
 }
 
@@ -223,9 +223,8 @@ static bool ast_get_vbios_mode_info(struct drm_crtc *crtc, struct drm_display_mo
 	}
 
 	return true;
-
-
 }
+
 static void ast_set_std_reg(struct drm_crtc *crtc, struct drm_display_mode *mode,
 			    struct ast_vbios_mode_info *vbios_mode)
 {
@@ -493,7 +492,6 @@ static void ast_set_start_address_crt1(struct drm_crtc *crtc, unsigned offset)
 	ast_set_index_reg(ast, AST_IO_CRTC_PORT, 0x0d, (u8)(addr & 0xff));
 	ast_set_index_reg(ast, AST_IO_CRTC_PORT, 0x0c, (u8)((addr >> 8) & 0xff));
 	ast_set_index_reg(ast, AST_IO_CRTC_PORT, 0xaf, (u8)((addr >> 16) & 0xff));
-
 }
 
 static void ast_crtc_dpms(struct drm_crtc *crtc, int mode)
@@ -644,9 +642,9 @@ static void ast_crtc_commit(struct drm_crtc *crtc)
 {
 	struct ast_private *ast = crtc->dev->dev_private;
 	ast_set_index_reg_mask(ast, AST_IO_SEQ_PORT, 0x1, 0xdf, 0);
+	ast_crtc_dpms(crtc, DRM_MODE_DPMS_ON);
 }
 
-
 static const struct drm_crtc_helper_funcs ast_crtc_helper_funcs = {
 	.dpms = ast_crtc_dpms,
 	.mode_set = ast_crtc_mode_set,
@@ -654,7 +652,6 @@ static const struct drm_crtc_helper_funcs ast_crtc_helper_funcs = {
 	.disable = ast_crtc_disable,
 	.prepare = ast_crtc_prepare,
 	.commit = ast_crtc_commit,
-
 };
 
 static void ast_crtc_reset(struct drm_crtc *crtc)
@@ -696,7 +693,7 @@ static int ast_crtc_init(struct drm_device *dev)
 		return -ENOMEM;
 
 	drm_crtc_init(dev, &crtc->base, &ast_crtc_funcs);
-	drm_mode_crtc_set_gamma_size(&crtc->base, 256);
+	drm_mode_crtc_set_gamma_size(&crtc->base, AST_GAMMA_LUT_SIZE);
 	drm_crtc_helper_add(&crtc->base, &ast_crtc_helper_funcs);
 	return 0;
 }
@@ -707,7 +704,6 @@ static void ast_encoder_destroy(struct drm_encoder *encoder)
 	kfree(encoder);
 }
 
-
 static struct drm_encoder *ast_best_single_encoder(struct drm_connector *connector)
 {
 	int enc_id = connector->encoder_ids[0];
@@ -731,6 +727,7 @@ static void ast_encoder_mode_set(struct drm_encoder *encoder,
 			       struct drm_display_mode *mode,
 			       struct drm_display_mode *adjusted_mode)
 {
+
 }
 
 static void ast_encoder_prepare(struct drm_encoder *encoder)
diff --git a/drivers/gpu/drm/ast/ast_tables.h b/drivers/gpu/drm/ast/ast_tables.h
index 5f4c2e8..6213e89 100644
--- a/drivers/gpu/drm/ast/ast_tables.h
+++ b/drivers/gpu/drm/ast/ast_tables.h
@@ -24,6 +24,8 @@
 #ifndef AST_TABLES_H
 #define AST_TABLES_H
 
+#define AST_GAMMA_LUT_SIZE	256
+
 /* Std. Table Index Definition */
 #define TextModeIndex		0
 #define EGAModeIndex		1
-- 
2.9.3


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