This series makes the amdgpu dma-buf exporter handle
AMDGPU_PL_MMIO_REMAP (the HDP flush page) as a BAR-mapped register
window (MMIO)
The HDP flush “MMIO_REMAP” page is a BAR-backed I/O window (not RAM).
When another PCIe device (GPU) needs to poke that window (e.g.,
device-to-device HDP flush), we must share it as a stable I/O span that
never migrates, and we must map it for importers using the correct API
for I/O resources (not page-backed memory).
This series makes MMIO_REMAP sharable through dma-buf by:
representing it as a singleton, pinned 4 KB BO for the device lifetime,
and mapping/unmapping it for importers via
dma_map_resource()/dma_unmap_resource() using a 1-entry sg_table
v2:
Design-level adjustments (Christian’s feedback):
- Pin at creation, not at export. We now pin the MMIO_REMAP BO in TTM
during init using ttm_bo_pin(). This enforces “never migrate/evict”
from birth and removes the need for export-time pinning and release-time
unpinning.
- No begin_cpu_access hacks. Since the object is pinned and treated as
fixed I/O, we removed the special-casing in begin_cpu_access();
migration heuristics are irrelevant.
- No pin/unpin no-ops in dma-buf paths. Those were a workaround for
export-time pinning. With creation-time pinning, they’re unnecessary
and are dropped.
* Only compilation tested so far (x86_64, defconfig + amdgpu enabled).
Suggested-by: Christian König <christian.koe...@amd.com>
Suggested-by: Alex Deucher <alexander.deuc...@amd.com>
Cc: Christian König <christian.koe...@amd.com>
Cc: Alex Deucher <alexander.deuc...@amd.com>
Srinivasan Shanmugam (3):
drm/amdgpu/ttm: Pin 4K MMIO_REMAP Singleton BO at Init
drm/amdgpu/dma-buf: Add helpers to map/unmap BAR I/O with
dma_map_resource()
drm/amdgpu/dma-buf: Map/Unmap MMIO_REMAP as BAR register window
(dma_map_resource)
drivers/gpu/drm/amd/amdgpu/amdgpu_dma_buf.c | 86 +++++++++++++++++++++
drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c | 26 +++++++
2 files changed, 112 insertions(+)
base-commit: bc52ed7845660e03827131505f95fcb4dd2fcf4f
--
2.34.1
