Re: [PATCH RESEND 1/4] drm/prime: Limit scatter list size with dedicated DMA device

From: Thomas Zimmermann

Date: Tue Mar 10 2026 - 04:00:26 EST




Am 10.03.26 um 04:25 schrieb Chen-Yu Tsai:
If a dedicated DMA device is specified for the DRM device, then the
scatter list size limit should pertain to the DMA device.

Use the dedicated DMA device, if given, to limit the scatter list size.
This only applies to drivers that have called drm_dev_set_dma_dev() and
are using drm_prime_pages_to_sg() either directly or through the SHMEM
helpers. At the time of this writing, the former case only includes the
Rockchip DRM driver, while the latter case includes the gud, udl, and
the tiny appletbdrm and gm12u320 drivers.

Signed-off-by: Chen-Yu Tsai <wenst@xxxxxxxxxxxx>

Reviewed-by: Thomas Zimmermann <tzimmermann@xxxxxxx>

---
drivers/gpu/drm/drm_prime.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/drm_prime.c b/drivers/gpu/drm/drm_prime.c
index 51fdb06d3e9f..9b44c78cd77f 100644
--- a/drivers/gpu/drm/drm_prime.c
+++ b/drivers/gpu/drm/drm_prime.c
@@ -859,7 +859,7 @@ struct sg_table *drm_prime_pages_to_sg(struct drm_device *dev,
return ERR_PTR(-ENOMEM);
if (dev)
- max_segment = dma_max_mapping_size(dev->dev);
+ max_segment = dma_max_mapping_size(drm_dev_dma_dev(dev));
if (max_segment == 0)
max_segment = UINT_MAX;
err = sg_alloc_table_from_pages_segment(sg, pages, nr_pages, 0,

--
--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Frankenstr. 146, 90461 Nürnberg, Germany, www.suse.com
GF: Jochen Jaser, Andrew McDonald, Werner Knoblich, (HRB 36809, AG Nürnberg)