Hi
Am 09.12.25 um 15:27 schrieb Boris Brezillon:
On Tue, 9 Dec 2025 14:41:57 +0100
Thomas Zimmermann <[email protected]> wrote:
Duplicate GEM-SHMEM to GEM-UMA. Convert all DRM drivers for UMA
systems if they currently use GEM-SHMEM.
Many DRM drivers for hardware with Unified Memory Architecture (UMA)
currently builds upon GEM-SHMEM and extends the helpers with features
for managing the GPU MMU. This allows the GPU to access the GEM buffer
content for its operation.
There is another, larger, set of DRM drivers that use GEM-SHMEM merely
as buffer management with no hardware support. These drivers copy the
buffer content to the GPU on each page flip. The GPU itself has no direct
access. Hardware of this type is usually in servers, behind slow busses
(SPI, USB), or provided by firmware (drivers in sysfb/).
After some discussion with Boris on the future of GEM-SHMEM, it seems
to me that both use cases more and more diverge from each other. The
most prominent example is the implementation of gem_prime_import,
where both use cases use distinct approaches.
So we discussed the introduction of a GEM-UMA helper library for
UMA-based hardware. GEM-UMA will remain flexible enough for drivers
to extend it for their use case. GEM-SHMEM will become focused on the
simple-hardware use case. The benefit for both libraries is that they
will be easier to understand and maintain. GEM-SHMEM can be simplified
signiifcantly, I think.
This RFC series introduces GEM-UMA and converts the UMA-related drivers.
Patches 1 and 2 fix issues in GEM-SHMEM, so that we don't duplicate
errornous code.
Patch 3 copies GEM-SHMEM to GEM-UMA. Patch 4 then does soem obvious
cleanups of unnecessary code.
Instead of copying the code as-is, I'd rather take a step back and think
about what we need and how we want to handle more complex stuff, like
reclaim. I've started working on a shrinker for panthor [1], and as part
of this series, I've added a commit implementing just enough to replace
what gem-shmem currently provides. Feels like the new GEM-UMA thing
could be designed on a composition rather than inheritance model,
where we have sub-components (backing, cpu_map, gpu_map) that can be
pulled in and re-used by the driver implementation. The common helpers
would take those sub-components instead of a plain GEM object. That
would leave the drivers free of how their internal gem_object fields are
laid out and wouldn't require overloading the ->gem_create_object()
function. It seems to be that it would better match the model you were
describing the other day.
Yeah, I've seen your update to that series. Making individual parts of
the memory manager freely composable with each other is a fine idea.
But the flipside is that I also want the simple drivers to move away
from the flexible approach that GEM-SHMEM currently takes. There are
many drivers that do not need or want that. These drivers benefit from
something that is self contained. Many of the drivers are also hardly
maintained, so simplifying things will also be helpful.
I could have added a new GEM implementation for these drivers, but there
are less UMA drivers to convert and the GEM-UMA naming generally fits
better than GEM-SHMEM.
I'd rather have GEM-UMA and evolve it from where it stands now; and also
evolve GEM-SHMEM in a different direction. There's a difference in
concepts here.
Best regards
Thomas
Patches 5 to 13 update the drivers that can be converted to GEM-UMA.
These changes are just symbol renaming. There are so far no functional
differences between the memory managers.
A gave GEM-UMA some smoke testing by running virtgpu.
[1]https://gitlab.freedesktop.org/bbrezillon/linux/-/commits/panthor-shrinker-revisited/drivers?ref_type=heads
[2]https://gitlab.freedesktop.org/bbrezillon/linux/-/commit/4e6927fc2c60265b77a5a88013f55377bc4f4ab3
Thomas Zimmermann (13):
drm/gem-shmem: Fix typos in documentation
drm/gem-shmem: Fix the MODULE_LICENSE() string
drm: Add GEM-UMA helpers for memory management
drm/gem-uma: Remove unused interfaces
drm/imagination: Use GEM-UMA helpers for memory management
drm/lima: Use GEM-UMA helpers for memory management
drm/panfrost: Use GEM-UMA helpers for memory management
drm/panthor: Use GEM-UMA helpers for memory management
drm/v3d: Use GEM-UMA helpers for memory management
drm/virtgpu: Use GEM-UMA helpers for memory management
accel/amdxdna: Use GEM-UMA helpers for memory management
accel/ivpu: Use GEM-UMA helpers for memory management
accel/rocket: Use GEM-UMA helpers for memory management
Documentation/gpu/drm-mm.rst | 12 +
drivers/accel/amdxdna/Kconfig | 2 +-
drivers/accel/amdxdna/aie2_ctx.c | 1 -
drivers/accel/amdxdna/aie2_message.c | 1 -
drivers/accel/amdxdna/aie2_pci.c | 1 -
drivers/accel/amdxdna/aie2_psp.c | 1 -
drivers/accel/amdxdna/aie2_smu.c | 1 -
drivers/accel/amdxdna/amdxdna_ctx.c | 7 +-
drivers/accel/amdxdna/amdxdna_gem.c | 49 +-
drivers/accel/amdxdna/amdxdna_gem.h | 5 +-
.../accel/amdxdna/amdxdna_mailbox_helper.c | 1 -
drivers/accel/amdxdna/amdxdna_pci_drv.c | 1 -
drivers/accel/amdxdna/amdxdna_sysfs.c | 1 -
drivers/accel/ivpu/Kconfig | 2 +-
drivers/accel/ivpu/ivpu_gem.c | 36 +-
drivers/accel/ivpu/ivpu_gem.h | 4 +-
drivers/accel/rocket/Kconfig | 2 +-
drivers/accel/rocket/rocket_gem.c | 46 +-
drivers/accel/rocket/rocket_gem.h | 6 +-
drivers/gpu/drm/Kconfig | 9 +
drivers/gpu/drm/Kconfig.debug | 1 +
drivers/gpu/drm/Makefile | 4 +
drivers/gpu/drm/drm_fbdev_uma.c | 203 +++++
drivers/gpu/drm/drm_gem_shmem_helper.c | 5 +-
drivers/gpu/drm/drm_gem_uma_helper.c | 787 ++++++++++++++++++
drivers/gpu/drm/imagination/Kconfig | 4 +-
drivers/gpu/drm/imagination/pvr_drv.c | 2 +-
drivers/gpu/drm/imagination/pvr_free_list.c | 2 +-
drivers/gpu/drm/imagination/pvr_gem.c | 74 +-
drivers/gpu/drm/imagination/pvr_gem.h | 12 +-
drivers/gpu/drm/lima/Kconfig | 4 +-
drivers/gpu/drm/lima/lima_drv.c | 2 +-
drivers/gpu/drm/lima/lima_gem.c | 30 +-
drivers/gpu/drm/lima/lima_gem.h | 6 +-
drivers/gpu/drm/panfrost/Kconfig | 2 +-
drivers/gpu/drm/panfrost/panfrost_drv.c | 2 +-
drivers/gpu/drm/panfrost/panfrost_gem.c | 30 +-
drivers/gpu/drm/panfrost/panfrost_gem.h | 6 +-
.../gpu/drm/panfrost/panfrost_gem_shrinker.c | 30 +-
drivers/gpu/drm/panfrost/panfrost_mmu.c | 8 +-
drivers/gpu/drm/panfrost/panfrost_perfcnt.c | 6 +-
drivers/gpu/drm/panthor/Kconfig | 2 +-
drivers/gpu/drm/panthor/panthor_drv.c | 2 +-
drivers/gpu/drm/panthor/panthor_fw.c | 4 +-
drivers/gpu/drm/panthor/panthor_gem.c | 40 +-
drivers/gpu/drm/panthor/panthor_gem.h | 8 +-
drivers/gpu/drm/panthor/panthor_mmu.c | 10 +-
drivers/gpu/drm/panthor/panthor_sched.c | 1 -
drivers/gpu/drm/tests/Makefile | 1 +
drivers/gpu/drm/tests/drm_gem_uma_test.c | 385 +++++++++
drivers/gpu/drm/v3d/Kconfig | 2 +-
drivers/gpu/drm/v3d/v3d_bo.c | 45 +-
drivers/gpu/drm/v3d/v3d_drv.h | 4 +-
drivers/gpu/drm/v3d/v3d_mmu.c | 9 +-
drivers/gpu/drm/virtio/Kconfig | 4 +-
drivers/gpu/drm/virtio/virtgpu_drv.c | 4 +-
drivers/gpu/drm/virtio/virtgpu_drv.h | 12 +-
drivers/gpu/drm/virtio/virtgpu_object.c | 64 +-
drivers/gpu/drm/virtio/virtgpu_plane.c | 6 +-
drivers/gpu/drm/virtio/virtgpu_vq.c | 6 +-
include/drm/drm_fbdev_uma.h | 20 +
include/drm/drm_gem_uma_helper.h | 293 +++++++
62 files changed, 2018 insertions(+), 312 deletions(-)
create mode 100644 drivers/gpu/drm/drm_fbdev_uma.c
create mode 100644 drivers/gpu/drm/drm_gem_uma_helper.c
create mode 100644 drivers/gpu/drm/tests/drm_gem_uma_test.c
create mode 100644 include/drm/drm_fbdev_uma.h
create mode 100644 include/drm/drm_gem_uma_helper.h
base-commit: 0a21e96e0b6840d2a4e0b45a957679eeddeb4362
prerequisite-patch-id: c67e5d886a47b7d0266d81100837557fda34cb24
prerequisite-patch-id: a5a973e527c88a5b47053d7a72aefe0b550197cb
prerequisite-patch-id: 719d09751d38f5da743beed6266585ee063e1e29
prerequisite-patch-id: 0bbc85bc6b528c32592e07f4ceafa51795c4cad9
prerequisite-patch-id: c856d9c8a026e3244c44ec829e426e0ad4a685ab
prerequisite-patch-id: 13441c9ed3062ae1448a53086559dfcbbd578177
prerequisite-patch-id: 951c039657c1f58e4b6e36bc01c7a1c69ed59767
prerequisite-patch-id: 4370b8b803ca439666fb9d2beb862f6e78347ce3
prerequisite-patch-id: ebbaad226ed599f7aad4784fb3f4aaebe34cb110
prerequisite-patch-id: cb907c3e3e14de7f4d13b429f3a2a88621a8a9fe
prerequisite-patch-id: 0e243b426742122b239af59e36d742da5795a8b1
prerequisite-patch-id: 120f97fa1af9891375a0dcf52c51c1907b01fe6a
--
--
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)
