[PATCH 1/3] drm/amdgpu: reserve 64M stolen memory for Apple 5K iMac

[Richard Lane <richardlanedev@gmail.com>]

Apple 27" 5K iMacs report a single 2560x2880 tile (28.125 MiB) in
VIEWPORT_SIZE while scanning out up to 64 MiB across the relocated EFI
framebuffer.

Override the stolen VGA memory allocation size to 64 MiB when matching
PCI_VENDOR_ID_APPLE with a 2560x2880x4 viewport size to prevent
framebuffer corruption during boot handover.

Signed-off-by: Richard Lane <richardlanedev@gmail.com>
---
 drivers/gpu/drm/amd/amdgpu/amdgpu_gmc.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_gmc.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_gmc.c
index 4204c3c750a8..8b196fbfa724 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_gmc.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_gmc.c
@@ -1232,7 +1232,15 @@ void amdgpu_gmc_init_vga_resv_regions(struct amdgpu_device *adev)
 	} else {
 		size = amdgpu_gmc_get_vbios_fb_size(adev);
 
-		if (adev->mman.keep_stolen_vga_memory)
+		/*
+		 * Apple 5K iMacs report one 2560x2880 tile in VIEWPORT_SIZE
+		 * while scanning out up to 64M across the relocated EFI
+		 * framebuffer.
+		 */
+		if (adev->pdev->subsystem_vendor == PCI_VENDOR_ID_APPLE &&
+		    size == (2560 * 2880 * 4))
+			size = 64U * 1024 * 1024;
+		else if (adev->mman.keep_stolen_vga_memory)
 			size = max(size, (unsigned)AMDGPU_VBIOS_VGA_ALLOCATION);
 	}
 
-- 
2.55.0