linux-kernel - [PATCH] drm/v3d: set the V3D GPU sg segment limitation

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Message-ID: <20251113092538.1971286-1-xiaolei.wang@windriver.com>
Date: Thu, 13 Nov 2025 17:25:38 +0800
From: Xiaolei Wang <xiaolei.wang@...driver.com>
To: mwen@...lia.com, mcanal@...lia.com, maarten.lankhorst@...ux.intel.com,
        mripard@...nel.org, tzimmermann@...e.de, airlied@...il.com,
        simona@...ll.ch, xiaolei.wang@...driver.com
Cc: dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: [PATCH] drm/v3d: set the V3D GPU sg segment limitation

When using V3D rendering, the kernel occasionally reports a
segment size mismatch. This is because 'max_seg_size' is not
set. The kernel defaults to 64K. Based on V3D's addressing
capabilities, setting 'max_seg_size' to the maximum will
prevent 'debug_dma_map_sg()' from complaining about the
over-mapping of the V3D segment length.

DMA-API: v3d 1002000000.v3d: mapping sg segment longer than device
 claims to support [len=8290304] [max=65536]
WARNING: CPU: 0 PID: 493 at kernel/dma/debug.c:1179 debug_dma_map_sg+0x330/0x388
CPU: 0 UID: 0 PID: 493 Comm: Xorg Not tainted 6.12.53-yocto-standard #1
Hardware name: Raspberry Pi 5 Model B Rev 1.0 (DT)
pstate: 60400009 (nZCv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--)
pc : debug_dma_map_sg+0x330/0x388
lr : debug_dma_map_sg+0x330/0x388
sp : ffff8000829a3ac0
x29: ffff8000829a3ac0 x28: 0000000000000001 x27: ffff8000813fe000
x26: ffffc1ffc0000000 x25: ffff00010fdeb760 x24: 0000000000000000
x23: ffff8000816a9bf0 x22: 0000000000000001 x21: 0000000000000002
x20: 0000000000000002 x19: ffff00010185e810 x18: ffffffffffffffff
x17: 69766564206e6168 x16: 74207265676e6f6c x15: 20746e656d676573
x14: 20677320676e6970 x13: 5d34303334393134 x12: 0000000000000000
x11: 00000000000000c0 x10: 00000000000009c0 x9 : ffff8000800e0b7c
x8 : ffff00010a315ca0 x7 : ffff8000816a5110 x6 : 0000000000000001
x5 : 000000000000002b x4 : 0000000000000002 x3 : 0000000000000008
x2 : 0000000000000000 x1 : 0000000000000000 x0 : ffff00010a315280
Call trace:
 debug_dma_map_sg+0x330/0x388
 __dma_map_sg_attrs+0xc0/0x278
 dma_map_sgtable+0x30/0x58
 drm_gem_shmem_get_pages_sgt+0xb4/0x140
 v3d_bo_create_finish+0x28/0x130 [v3d]
 v3d_create_bo_ioctl+0x54/0x180 [v3d]
 drm_ioctl_kernel+0xc8/0x140
 drm_ioctl+0x2d4/0x4d8

Signed-off-by: Xiaolei Wang <xiaolei.wang@...driver.com>
---
 drivers/gpu/drm/v3d/v3d_drv.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/gpu/drm/v3d/v3d_drv.c b/drivers/gpu/drm/v3d/v3d_drv.c
index c5a3bbbc74c5..f4da7a94e401 100644
--- a/drivers/gpu/drm/v3d/v3d_drv.c
+++ b/drivers/gpu/drm/v3d/v3d_drv.c
@@ -377,6 +377,8 @@ static int v3d_platform_drm_probe(struct platform_device *pdev)
 	if (ret)
 		goto clk_disable;
 
+	dma_set_max_seg_size(&pdev->dev, UINT_MAX);
+
 	v3d->va_width = 30 + V3D_GET_FIELD(mmu_debug, V3D_MMU_VA_WIDTH);
 
 	ident1 = V3D_READ(V3D_HUB_IDENT1);
-- 
2.43.0