FAILED: patch "[PATCH] fbdev: vesafb: Detect VGA compatibility from screen info's" failed to apply to 6.6-stable tree

The patch below does not apply to the 6.6-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.6.y
git checkout FETCH_HEAD
git cherry-pick -x c2bc958b2b03e361f14df99983bc64a39a7323a3
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2024072945-reenter-waving-4e70@gregkh' --subject-prefix 'PATCH 6.6.y' HEAD^..

Possible dependencies:

c2bc958b2b03 ("fbdev: vesafb: Detect VGA compatibility from screen info's VESA attributes") 75fa9b7e375e ("video: Add helpers for decoding screen_info")
3218286bbb78 ("fbdev/vesafb: Replace references to global screen_info by local pointer")

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From c2bc958b2b03e361f14df99983bc64a39a7323a3 Mon Sep 17 00:00:00 2001
From: Thomas Zimmermann <[email protected]>
Date: Mon, 17 Jun 2024 13:06:27 +0200
Subject: [PATCH] fbdev: vesafb: Detect VGA compatibility from screen info's
VESA attributes

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.

index 8ab64ae4cad3..5a161750a3ae 100644
@@ -271,7 +271,7 @@ 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)

index 75303c126285..6a4a3cec4638 100644
@@ -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) {