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pan/kmod: Allow mmap() on foreign buffers

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If the BO comes from a different subsystem
(args.extra_flags & DRM_PANTHOR_BO_IS_IMPORTED), we should normally
add extra DMA_BUF_IOCTL_SYNC calls around CPU accesses to ensure the
CPU mapping consistency, but this is something we never worried about
(we've always assumed exporters were exposing uncached mappings with
NOP {begin,end}_cpu_access() implementations), and it worked fine until
now.

The long term plan is to hook up DMA_BUF_IOCTL_SYNC, but this requires
more work, and we need a quick fix that can be backported easily, hence
this revert+FIXME.

Fixes: b5e47ba894 ("pan/kmod: Add new helpers to sync BO CPU mappings")
Closes: https://gitlab.freedesktop.org/mesa/mesa/-/issues/14963
Closes: https://gitlab.freedesktop.org/panfrost/mesa/-/issues/282
Closes: https://gitlab.freedesktop.org/wayland/weston/-/issues/1101
Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>
Reviewed-by: Yiwei Zhang <zzyiwei@chromium.org>
Acked-by: Lars-Ivar Hesselberg Simonsen <lars-ivar.simonsen@arm.com>
Acked-by: Erik Faye-Lund <erik.faye-lund@collabora.com>
Reviewed-by: Daniel Stone <daniels@collabora.com>
(cherry picked from commit 30f1d5bab9)

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/40359>
This commit is contained in:
Boris Brezillon 2026-03-03 17:31:16 +01:00 • committed by Eric Engestrom
parent b299e0323a
commit 7ee55d3a5f
3 changed files with 19 additions and 9 deletions
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2
.pick_status.json
View file

@ -3484,7 +3484,7 @@
"description": "pan/kmod: Allow mmap() on foreign buffers",
"nominated": true,
"nomination_type": 2,
"resolution": 0,
"resolution": 1,
"main_sha": null,
"because_sha": "b5e47ba8941467a4e2f53907a6645a0703852e62",
"notes": null

13
src/panfrost/lib/kmod/panfrost_kmod.c
View file

@ -350,11 +350,16 @@ panfrost_kmod_bo_import(struct pan_kmod_dev *dev, uint32_t handle, uint64_t size
goto err_free_bo;
}
/* If the BO comes from a different subsystem, we don't allow
* mmap() to avoid the CPU-sync churn.
/* FIXME: If the BO comes from a different subsystem
* (args.extra_flags & DRM_PANTHOR_BO_IS_IMPORTED), we should normally
* add extra DMA_BUF_IOCTL_SYNC calls around CPU accesses to ensure the
* CPU mapping consistency, but this is something we never worried about
* (we've always assumed exporters were exposing uncached mappings with
* NOP {begin,end}_cpu_access() implementations), and it worked fine until
* now.
* The long term plan is to hook up DMA_BUF_IOCTL_SYNC, but this requires
* more work.
*/
if (args.extra_flags & DRM_PANFROST_BO_IS_IMPORTED)
flags |= PAN_KMOD_BO_FLAG_NO_MMAP;
}
pan_kmod_bo_init(&panfrost_bo->base, dev, NULL, size,

13
src/panfrost/lib/kmod/panthor_kmod.c
View file

@ -445,11 +445,16 @@ panthor_kmod_bo_import(struct pan_kmod_dev *dev, uint32_t handle, uint64_t size,
goto err_free_bo;
}
/* If the BO comes from a different subsystem, we don't allow
* mmap() to avoid the CPU-sync churn.
/* FIXME: If the BO comes from a different subsystem
* (args.extra_flags & DRM_PANTHOR_BO_IS_IMPORTED), we should normally
* add extra DMA_BUF_IOCTL_SYNC calls around CPU accesses to ensure the
* CPU mapping consistency, but this is something we never worried about
* (we've always assumed exporters were exposing uncached mappings with
* NOP {begin,end}_cpu_access() implementations), and it worked fine until
* now.
* The long term plan is to hook up DMA_BUF_IOCTL_SYNC, but this requires
* more work.
*/
if (args.extra_flags & DRM_PANTHOR_BO_IS_IMPORTED)
flags |= PAN_KMOD_BO_FLAG_NO_MMAP;
}
/* Create a unsignalled syncobj on import. Will serve as a