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fbdev: vesafb: Detect VGA compatibility from screen info's VESA attributes

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BugLink: https://bugs.launchpad.net/bugs/2083196

commit c2bc958b2b03e361f14df99983bc64a39a7323a3 upstream.

Test the vesa_attributes field in struct screen_info for compatibility
with VGA hardware. Vesafb currently tests bit 1 in screen_info's
capabilities field which indicates a 64-bit lfb address and is
unrelated to VGA compatibility.

Section 4.4 of the Vesa VBE 2.0 specifications defines that bit 5 in
the mode's attributes field signals VGA compatibility. The mode is
compatible with VGA hardware if the bit is clear. In that case, the
driver can access VGA state of the VBE's underlying hardware. The
vesafb driver uses this feature to program the color LUT in palette
modes. Without, colors might be incorrect.

The problem got introduced in commit 89ec4c238e ("[PATCH] vesafb: Fix
incorrect logo colors in x86_64"). It incorrectly stores the mode
attributes in the screen_info's capabilities field and updates vesafb
accordingly. Later, commit 5e8ddcbe86 ("Video mode probing support for
the new x86 setup code") fixed the screen_info, but did not update vesafb.
Color output still tends to work, because bit 1 in capabilities is
usually 0.

Besides fixing the bug in vesafb, this commit introduces a helper that
reads the correct bit from screen_info.

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Fixes: 5e8ddcbe86 ("Video mode probing support for the new x86 setup code")
Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>
Cc: <stable@vger.kernel.org> # v2.6.23+
Signed-off-by: Helge Deller <deller@gmx.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
[portias: Add #include <linux/bits.h>]
Signed-off-by: Portia Stephens <portia.stephens@canonical.com>
Signed-off-by: Roxana Nicolescu <roxana.nicolescu@canonical.com>
This commit is contained in:
Thomas Zimmermann
2024-06-17 13:06:27 +02:00
committed by Mehmet Basaran
parent 633d21e907
commit 80084b8445
2 changed files with 13 additions and 1 deletions
Download Patch File Download Diff File Expand all files Collapse all files
drivers/video/fbdev/vesafb.c
+1 -1
View File
@@ -258,7 +258,7 @@ static int vesafb_probe(struct platform_device *dev)
if (screen_info.orig_video_isVGA != VIDEO_TYPE_VLFB)
return -ENODEV;
vga_compat = (screen_info.capabilities & 2) ? 0 : 1;
vga_compat = !__screen_info_vbe_mode_nonvga(si);
vesafb_fix.smem_start = screen_info.lfb_base;
vesafb_defined.bits_per_pixel = screen_info.lfb_depth;
if (15 == vesafb_defined.bits_per_pixel)
include/linux/screen_info.h
+12
View File
@@ -4,6 +4,18 @@
#include <uapi/linux/screen_info.h>
#include <linux/bits.h>
extern struct screen_info screen_info;
static inline bool __screen_info_vbe_mode_nonvga(const struct screen_info *si)
{
/*
* VESA modes typically run on VGA hardware. Set bit 5 signals that this
* is not the case. Drivers can then not make use of VGA resources. See
* Sec 4.4 of the VBE 2.0 spec.
*/
return si->vesa_attributes & BIT(5);
}
#endif /* _SCREEN_INFO_H */