Re: PROBLEM: AST2500 BMC video output disabled by reboot (regression)

[Thomas Zimmermann <tzimmermann@suse.de>]

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Hi

Am 18.09.25 um 04:04 schrieb Nick Bowler:
> On Wed, Sep 17, 2025 at 11:14:45AM -0400, Nick Bowler wrote:
>> On Fri, Aug 29, 2025 at 03:07:14PM +0200, Thomas Zimmermann wrote:
>>> The ast driver doesn't do much during shutdown. Could you please out-comment
>>> the lines at either [2] xor [3] and report on either effect? These calls
>>> turn of the video chip's memory access and sync pulses. Not doing that might
>>> resolve the problem.
>>>
>>> [2] https://elixir.bootlin.com/linux/v6.16.3/source/drivers/gpu/drm/ast/ast_mode.c#L835
>>> [3] https://elixir.bootlin.com/linux/v6.16.3/source/drivers/gpu/drm/ast/ast_mode.c#L839
>> I can try this.
> OK, I tested 6.17-rc6 and reproduced the problem on this version.  Then:
>
>    - Deleting [2] (only) appears to make no difference whatsoever. That
>      is, deleting the following line in ast_mode.c:
>
>        ast_set_index_reg_mask(ast, AST_IO_VGASRI, 0x01, 0xdf, AST_IO_VGASR1_SD);
>
>    - Deleting [3] (only) appears sufficient to make things work again,
>      that is, deleting the following line in ast_mode.c:
>
>        ast_set_index_reg_mask(ast, AST_IO_VGACRI, 0xb6, 0xfc, vgacrb6);

Please test if the attached patch fixes the problem for you.

Best regards
Thomas

>
> Thanks,
>    Nick

-- 
--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Frankenstrasse 146, 90461 Nuernberg, Germany
GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman
HRB 36809 (AG Nuernberg)


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From 51ebb573a090494de79cbb71e9b29255e1364e1c Mon Sep 17 00:00:00 2001
From: Thomas Zimmermann <tzimmermann@suse.de>
Date: Thu, 18 Sep 2025 09:50:28 +0200
Subject: [PATCH] ast: Use VGACR17 sync enable

Blank the display by disabling sync pulses with VGACR17<7>. Some
BMC's don't handle VGACRB6 correctly. And don't modify VGASR1's SD
bit, which only disables GPU access to VRAM.
---
 drivers/gpu/drm/ast/ast_mode.c | 14 ++++++--------
 drivers/gpu/drm/ast/ast_reg.h  |  1 +
 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 b4e8edc7c767..0df06de9b644 100644
--- a/drivers/gpu/drm/ast/ast_mode.c
+++ b/drivers/gpu/drm/ast/ast_mode.c
@@ -836,22 +836,20 @@ ast_crtc_helper_atomic_flush(struct drm_crtc *crtc,
 static void ast_crtc_helper_atomic_enable(struct drm_crtc *crtc, struct drm_atomic_state *state)
 {
 	struct ast_device *ast = to_ast_device(crtc->dev);
+	u8 vgacr17 = 0x00;
 
-	ast_set_index_reg_mask(ast, AST_IO_VGACRI, 0xb6, 0xfc, 0x00);
-	ast_set_index_reg_mask(ast, AST_IO_VGASRI, 0x01, 0xdf, 0x00);
+	vgacr17 |= AST_IO_VGACR17_SYNC_ENABLE;
+	ast_set_index_reg_mask(ast, AST_IO_VGACRI, 0x17, 0x7f, vgacr17);
 }
 
 static void ast_crtc_helper_atomic_disable(struct drm_crtc *crtc, struct drm_atomic_state *state)
 {
 	struct drm_crtc_state *old_crtc_state = drm_atomic_get_old_crtc_state(state, crtc);
 	struct ast_device *ast = to_ast_device(crtc->dev);
-	u8 vgacrb6;
+	u8 vgacr17 = 0xff;
 
-	ast_set_index_reg_mask(ast, AST_IO_VGASRI, 0x01, 0xdf, AST_IO_VGASR1_SD);
-
-	vgacrb6 = AST_IO_VGACRB6_VSYNC_OFF |
-		  AST_IO_VGACRB6_HSYNC_OFF;
-	ast_set_index_reg_mask(ast, AST_IO_VGACRI, 0xb6, 0xfc, vgacrb6);
+	vgacr17 &= ~AST_IO_VGACR17_SYNC_ENABLE;
+	ast_set_index_reg_mask(ast, AST_IO_VGACRI, 0x17, 0x7f, vgacr17);
 
 	/*
 	 * HW cursors require the underlying primary plane and CRTC to
diff --git a/drivers/gpu/drm/ast/ast_reg.h b/drivers/gpu/drm/ast/ast_reg.h
index e15adaf3a80e..30578e3b07e4 100644
--- a/drivers/gpu/drm/ast/ast_reg.h
+++ b/drivers/gpu/drm/ast/ast_reg.h
@@ -29,6 +29,7 @@
 #define AST_IO_VGAGRI			(0x4E)
 
 #define AST_IO_VGACRI			(0x54)
+#define AST_IO_VGACR17_SYNC_ENABLE	BIT(7) /* called "Hardware reset" in docs */
 #define AST_IO_VGACR80_PASSWORD		(0xa8)
 #define AST_IO_VGACR99_VGAMEM_RSRV_MASK	GENMASK(1, 0)
 #define AST_IO_VGACRA1_VGAIO_DISABLED	BIT(1)
-- 
2.51.0