# --- T2-COPYRIGHT-BEGIN ---
# t2/package/*/linux/hotfix-radeon-ppc-agp.patch
# Copyright (C) 2026 The T2 SDE Project
# SPDX-License-Identifier: GPL-2.0 or patched project license
# --- T2-COPYRIGHT-END ---

From: René Rebe <rene@exactco.de>
Subject: [PATCH] drm/radeon: default to AGP on PowerMac

On Apple PowerMac G4 r1xx/r2xx the PCI/AIC GART path intermittently stalls
the CP's register delivery to the 2D engine under load and hard locks the
machine, whereas AGP appears to be stable.

Upstream defaults radeon_agpmode to -1 (force PCI) for x86-stability
reasons, which is the wrong default for this hardware.  So when running
on a PowerMac (runtime machine_is(powermac) check, not just a PMAC-enabled
kernel), promote the untouched default (-1) to auto (0) for AGP-capable
asics, using the bridge-negotiated AGP mode.  An explicit user agpmode=
still takes effect; to force PCI, blacklist the uninorth-agp driver.

Signed-off-by: René Rebe <rene@exactco.de>

--- a/drivers/gpu/drm/radeon/radeon_device.c
+++ b/drivers/gpu/drm/radeon/radeon_device.c
@@ -33,6 +33,10 @@
 #include <linux/vga_switcheroo.h>
 #include <linux/vgaarb.h>

+#ifdef CONFIG_PPC_PMAC
+#include <asm/machdep.h>
+#endif
+
 #include <drm/drm_cache.h>
 #include <drm/drm_client_event.h>
 #include <drm/drm_crtc_helper.h>
@@ -1338,6 +1342,16 @@
 		rdev->flags &= ~RADEON_IS_AGP;
 	}

+	/*
+	 * On PowerMac (UniNorth/U3 AGP bridges) the on-chip PCI/AIC GART path is
+	 * unreliable on r1xx/r2xx: it intermittently stalls the CP.
+	 */
+#ifdef CONFIG_PPC_PMAC
+	if (machine_is(powermac) &&
+	    (rdev->flags & RADEON_IS_AGP) && radeon_agpmode == -2)
+		radeon_agpmode = 0;
+#endif
+
 	if (rdev->flags & RADEON_IS_AGP && radeon_agpmode == -1) {
 		radeon_agp_disable(rdev);
 	}
--- linux-7.1/drivers/gpu/drm/radeon/radeon_device.c.vanilla	2026-07-19 21:01:20.344596200 +0200
+++ linux-7.1/drivers/gpu/drm/radeon/radeon_device.c	2026-07-19 21:33:37.711260839 +0200
@@ -1139,6 +1139,7 @@
 
 	/* AGP mode can only be -1, 1, 2, 4, 8 */
 	switch (radeon_agpmode) {
+	case -2:
 	case -1:
 	case 0:
 	case 1:
@@ -1338,7 +1339,7 @@
 		rdev->flags &= ~RADEON_IS_AGP;
 	}
 
-	if (rdev->flags & RADEON_IS_AGP && radeon_agpmode == -1) {
+	if (rdev->flags & RADEON_IS_AGP && radeon_agpmode < 0) {
 		radeon_agp_disable(rdev);
 	}
 
--- linux-7.1/drivers/gpu/drm/radeon/radeon_drv.c.vanilla	2026-07-19 21:31:21.870509292 +0200
+++ linux-7.1/drivers/gpu/drm/radeon/radeon_drv.c	2026-07-19 21:31:48.177398186 +0200
@@ -120,7 +120,7 @@
 int radeon_modeset = -1;
 int radeon_dynclks = -1;
 int radeon_r4xx_atom;
-int radeon_agpmode = -1;
+int radeon_agpmode = -2;
 int radeon_vram_limit;
 int radeon_gart_size = -1; /* auto */
 int radeon_benchmarking;