linux-kernel - [PATCH V2] drm/mgag200: Fix big-endian support

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Message-Id: <20251205.182405.876575799174263183.rene@exactco.de>
Date: Fri, 05 Dec 2025 18:24:05 +0100 (CET)
From: René Rebe <rene@...ctco.de>
To: dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Cc: Dave Airlie <airlied@...hat.com>, Thomas Zimmermann
 <tzimmermann@...e.de>
Subject: [PATCH V2] drm/mgag200: Fix big-endian support

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@...ctco.de>
Cc: stable@...nel.org
---
V2: move to atomic_update
Tested on IBM 43p Model 150 (7043-150) running T2/Linux.
---
 drivers/gpu/drm/mgag200/mgag200_mode.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/drivers/gpu/drm/mgag200/mgag200_mode.c b/drivers/gpu/drm/mgag200/mgag200_mode.c
index 951d715dea30..d40434ec68ab 100644
--- a/drivers/gpu/drm/mgag200/mgag200_mode.c
+++ b/drivers/gpu/drm/mgag200/mgag200_mode.c
@@ -496,6 +496,20 @@ void mgag200_primary_plane_helper_atomic_update(struct drm_plane *plane,
 	struct drm_atomic_helper_damage_iter iter;
 	struct drm_rect damage;
 
+#ifdef __BIG_ENDIAN
+	/* Big-endian byte-swapping */
+	switch (fb->format->format) {
+	case DRM_FORMAT_RGB565:
+		WREG32(MGAREG_OPMODE, 0x10100);
+		break;
+	case DRM_FORMAT_XRGB8888:
+		WREG32(MGAREG_OPMODE, 0x20200);
+		break;
+	default:
+		break;
+	}
+#endif
+
 	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);
-- 
2.52.0

-- 
René Rebe, ExactCODE GmbH, Berlin, Germany
https://exactco.de • https://t2linux.com • https://patreon.com/renerebe