From 340bbe90cc7d0fe27018907c217d42cee4b2ca93 Mon Sep 17 00:00:00 2001 From: Thomas Zimmermann Date: Mon, 17 Jun 2024 13:06:27 +0200 Subject: [PATCH] fbdev: vesafb: Detect VGA compatibility from screen info's VESA attributes [ Upstream commit c2bc958b2b03e361f14df99983bc64a39a7323a3 ] 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 89ec4c238e7a ("[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 5e8ddcbe8692 ("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 Fixes: 5e8ddcbe8692 ("Video mode probing support for the new x86 setup code") Reviewed-by: Javier Martinez Canillas Cc: # v2.6.23+ Signed-off-by: Helge Deller Signed-off-by: Sasha Levin --- drivers/video/fbdev/vesafb.c | 2 +- include/linux/screen_info.h | 10 ++++++++++ 2 files changed, 11 insertions(+), 1 deletion(-) diff --git a/drivers/video/fbdev/vesafb.c b/drivers/video/fbdev/vesafb.c index ea89accbec38..a21581b40256 100644 --- a/drivers/video/fbdev/vesafb.c +++ b/drivers/video/fbdev/vesafb.c @@ -259,7 +259,7 @@ static int vesafb_probe(struct platform_device *dev) if (si->orig_video_isVGA != VIDEO_TYPE_VLFB) return -ENODEV; - vga_compat = (si->capabilities & 2) ? 0 : 1; + vga_compat = !__screen_info_vbe_mode_nonvga(si); vesafb_fix.smem_start = si->lfb_base; vesafb_defined.bits_per_pixel = si->lfb_depth; if (15 == vesafb_defined.bits_per_pixel) diff --git a/include/linux/screen_info.h b/include/linux/screen_info.h index 75303c126285..6a4a3cec4638 100644 --- a/include/linux/screen_info.h +++ b/include/linux/screen_info.h @@ -49,6 +49,16 @@ static inline u64 __screen_info_lfb_size(const struct screen_info *si, unsigned return lfb_size; } +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); +} + static inline unsigned int __screen_info_video_type(unsigned int type) { switch (type) {