linux-kernel - [PATCH v2 1/1] drm/ttm: allocate dummy_read

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Date: Wed, 17 Jan 2024 02:50:34 +0800
From: Yangyu Chen <cyy@...self.name>
To: dri-devel@...ts.freedesktop.org
Cc: linux-kernel@...r.kernel.org,
	Christian Koenig <christian.koenig@....com>,
	Huang Rui <ray.huang@....com>,
	Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
	Maxime Ripard <mripard@...nel.org>,
	Thomas Zimmermann <tzimmermann@...e.de>,
	David Airlie <airlied@...il.com>,
	Daniel Vetter <daniel@...ll.ch>,
	Jiuyang Liu <liu@...yang.me>,
	Yichuan Gao <i@...is.me>,
	Icenowy Zheng <uwu@...nowy.me>,
	Yangyu Chen <cyy@...self.name>
Subject: [PATCH v2 1/1] drm/ttm: allocate dummy_read_page without DMA32 on fail

Some platforms may not have any memory in ZONE_DMA32 and use IOMMU to allow
32-bit-DMA-only device to work. Forcing GFP_DMA32 on dummy_read_page will
fail on such platforms. Retry after fail will get this works on such
platforms.

Signed-off-by: Yangyu Chen <cyy@...self.name>
---
 drivers/gpu/drm/ttm/ttm_device.c | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/ttm/ttm_device.c b/drivers/gpu/drm/ttm/ttm_device.c
index d48b39132b32..c9fa8561f71f 100644
--- a/drivers/gpu/drm/ttm/ttm_device.c
+++ b/drivers/gpu/drm/ttm/ttm_device.c
@@ -95,11 +95,17 @@ static int ttm_global_init(void)
 	ttm_pool_mgr_init(num_pages);
 	ttm_tt_mgr_init(num_pages, num_dma32);
 
-	glob->dummy_read_page = alloc_page(__GFP_ZERO | GFP_DMA32);
+	glob->dummy_read_page = alloc_page(__GFP_ZERO | GFP_DMA32 |
+					   __GFP_NOWARN);
 
+	/* Retry without GFP_DMA32 for platforms DMA32 is not available */
 	if (unlikely(glob->dummy_read_page == NULL)) {
-		ret = -ENOMEM;
-		goto out;
+		glob->dummy_read_page = alloc_page(__GFP_ZERO);
+		if (unlikely(glob->dummy_read_page == NULL)) {
+			ret = -ENOMEM;
+			goto out;
+		}
+		pr_warn("Using GFP_DMA32 fallback for dummy_read_page\n");
 	}
 
 	INIT_LIST_HEAD(&glob->device_list);
-- 
2.43.0