linux-kernel - [PATCH V3] drm/mgag200: Fix big-endian support

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Message-Id: <20251208.141827.965103015954471168.rene@exactco.de>
Date: Mon, 08 Dec 2025 14:18:27 +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 V3] 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
---
V3: move to func, mask prev reg content
V2: move to atomic_update
V3 was only compile tested, while V1/2 were tested on IBM 43p w/ T2/Linux.
---
 drivers/gpu/drm/mgag200/mgag200_mode.c | 24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)

diff --git a/drivers/gpu/drm/mgag200/mgag200_mode.c b/drivers/gpu/drm/mgag200/mgag200_mode.c
index 951d715dea30..191037ce1029 100644
--- a/drivers/gpu/drm/mgag200/mgag200_mode.c
+++ b/drivers/gpu/drm/mgag200/mgag200_mode.c
@@ -161,6 +161,29 @@ 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 __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 +519,7 @@ 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);
-- 
2.52.0

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