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From 4bfb389a0136a13f0802eeb5e97a0e76d88f77ae Mon Sep 17 00:00:00 2001
From: Thomas Zimmermann <tzimmermann@suse.de>
Date: Fri, 28 Mar 2025 10:17:05 +0100
Subject: drm/cirrus-qemu: Fix pitch programming
From: Thomas Zimmermann <tzimmermann@suse.de>
commit 4bfb389a0136a13f0802eeb5e97a0e76d88f77ae upstream.
Do not set CR1B[6] when programming the pitch. The bit effects VGA
text mode and is not interpreted by qemu. [1] It has no affect on
the scanline pitch.
The scanline bit that is set into CR1B[6] belongs into CR13[7], which
the driver sets up correctly.
This bug goes back to the driver's initial commit.
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Acked-by: Gerd Hoffmann <kraxel@redhat.com>
Link: https://gitlab.com/qemu-project/qemu/-/blob/stable-9.2/hw/display/cirrus_vga.c?ref_type=heads#L1112 # 1
Fixes: f9aa76a85248 ("drm/kms: driver for virtual cirrus under qemu")
Cc: Adam Jackson <ajax@redhat.com>
Cc: Dave Airlie <airlied@redhat.com>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Maxime Ripard <mripard@kernel.org>
Cc: Thomas Zimmermann <tzimmermann@suse.de>
Cc: <stable@vger.kernel.org> # v3.5+
Link: https://lore.kernel.org/r/20250328091821.195061-2-tzimmermann@suse.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/gpu/drm/tiny/cirrus.c | 1 -
1 file changed, 1 deletion(-)
--- a/drivers/gpu/drm/tiny/cirrus.c
+++ b/drivers/gpu/drm/tiny/cirrus.c
@@ -318,7 +318,6 @@ static void cirrus_pitch_set(struct cirr
/* Enable extended blanking and pitch bits, and enable full memory */
cr1b = 0x22;
cr1b |= (pitch >> 7) & 0x10;
- cr1b |= (pitch >> 6) & 0x40;
wreg_crt(cirrus, 0x1b, cr1b);
cirrus_set_start_address(cirrus, 0);
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