FAILED: patch "[PATCH] drm/mgag200: Fix big-endian support" failed to apply to 5.15-stable tree

[<gregkh@linuxfoundation.org>]

The patch below does not apply to the 5.15-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 <stable@vger.kernel.org>.

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-5.15.y
git checkout FETCH_HEAD
git cherry-pick -x 6cb31fba137d45e682ce455b8ea364f44d5d4f98
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@vger.kernel.org>' --in-reply-to '2026010546-doorpost-resume-e2e2@gregkh' --subject-prefix 'PATCH 5.15.y' HEAD^..

Possible dependencies:



thanks,

greg k-h

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

From 6cb31fba137d45e682ce455b8ea364f44d5d4f98 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Ren=C3=A9=20Rebe?= <rene@exactco.de>
Date: Mon, 8 Dec 2025 14:18:27 +0100
Subject: [PATCH] drm/mgag200: Fix big-endian support
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

Unlike the original, deleted Matrox mga driver, the new mgag200 driver
has the XRGB frame-buffer byte swapped on big-endian "RISC"
systems. Fix by enabling byte swapping "PowerPC" OPMODE for any
__BIG_ENDIAN config.

Fixes: 414c45310625 ("mgag200: initial g200se driver (v2)")
Signed-off-by: René Rebe <rene@exactco.de>
Cc: stable@kernel.org
Reviewed-by: Thomas Zimmermann <tzimmermann@suse.de>
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Link: https://patch.msgid.link/20251208.141827.965103015954471168.rene@exactco.de

diff --git a/drivers/gpu/drm/mgag200/mgag200_mode.c b/drivers/gpu/drm/mgag200/mgag200_mode.c
index 951d715dea30..d019177462cf 100644
--- a/drivers/gpu/drm/mgag200/mgag200_mode.c
+++ b/drivers/gpu/drm/mgag200/mgag200_mode.c
@@ -161,6 +161,30 @@ static void mgag200_set_startadd(struct mga_device *mdev,
 	WREG_ECRT(0x00, crtcext0);
 }
 
+/*
+ * Set the opmode for the hardware swapper for Big-Endian processor
+ * support for the frame buffer aperture and DMAWIN space.
+ */
+static void mgag200_set_datasiz(struct mga_device *mdev, u32 format)
+{
+#if defined(__BIG_ENDIAN)
+	u32 opmode = RREG32(MGAREG_OPMODE);
+
+	opmode &= ~(GENMASK(17, 16) | GENMASK(9, 8) | GENMASK(3, 2));
+
+	/* Big-endian byte-swapping */
+	switch (format) {
+	case DRM_FORMAT_RGB565:
+		opmode |= 0x10100;
+		break;
+	case DRM_FORMAT_XRGB8888:
+		opmode |= 0x20200;
+		break;
+	}
+	WREG32(MGAREG_OPMODE, opmode);
+#endif
+}
+
 void mgag200_init_registers(struct mga_device *mdev)
 {
 	u8 crtc11, misc;
@@ -496,6 +520,7 @@ void mgag200_primary_plane_helper_atomic_update(struct drm_plane *plane,
 	struct drm_atomic_helper_damage_iter iter;
 	struct drm_rect damage;
 
+	mgag200_set_datasiz(mdev, fb->format->format);
 	drm_atomic_helper_damage_iter_init(&iter, old_plane_state, plane_state);
 	drm_atomic_for_each_plane_damage(&iter, &damage) {
 		mgag200_handle_damage(mdev, shadow_plane_state->data, fb, &damage);