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

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Message-Id: <20251202.164228.1439289308743755090.rene@exactco.de>
Date: Tue, 02 Dec 2025 16:42:28 +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] drm/mgag200: fix big-endian support

Unlike the original deleted Matrox mga driver, the new mgag200 driver
has the frame-buffer RGBX 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>
---
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..9073063f6473 100644
--- a/drivers/gpu/drm/mgag200/mgag200_mode.c
+++ b/drivers/gpu/drm/mgag200/mgag200_mode.c
@@ -655,6 +655,20 @@ void mgag200_crtc_helper_atomic_enable(struct drm_crtc *crtc, struct drm_atomic_
 	else
 		mgag200_crtc_fill_gamma(mdev, format);
 
+#ifdef __BIG_ENDIAN
+	/* Big-endian byte-swapping */
+	switch (format->format) {
+	case DRM_FORMAT_RGB565:
+		WREG32(MGAREG_OPMODE, 1 << 16);
+		break;
+	case DRM_FORMAT_XRGB8888:
+		WREG32(MGAREG_OPMODE, 2 << 16);
+		break;
+	default:
+		break;
+	}
+#endif
+
 	mgag200_enable_display(mdev);
 }
 
-- 
2.46.0

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