Change order of linkage in kernel makefiles for amdkfd
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| # | Subject and files | Size | Replies | Applied |
|---|---|---|---|---|
| 1/2 | drivers: Move iommu/ before gpu/ in Makefiledrivers/ | +4 | 2 replies | |
| 2/2 | drm: Put amdkfd before radeon in drm Makefiledrivers/ | +1 | 0 replies |
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Cover letter [PATCH 0/2] Change order of linkage in kernel makefiles for amdkfd
This small patch-set, was created to solve the bug described at
https://bugzilla.kernel.org/show_bug.cgi?id=89661 (Kernel panic when trying use amdkfd driver on Kaveri). It replaces the previous patch-set called [PATCH 0/3] Use workqueue for device init in amdkfd
(http://lists.freedesktop.org/archives/dri-devel/2014-December/074401.html)
That bug appears only when radeon, amdkfd and amd_iommu_v2 are compiled inside the kernel (not as modules). In that case, the correct loading order, as determined by the exported symbol used by each driver, is not enforced anymore and the kernel loads them based on who was linked first. That makes radeon load first, amdkfd second and amd_iommu_v2 third.
Because the initialization of a device in amdkfd is initiated by radeon, and can only be completed if amdkfd and amd_iommu_v2 were loaded and initialized, then in the case mentioned above, this initalization fails and there is a kernel panic as some pointers are not initialized but used nontheless.
To solve this bug, this patch-set moves iommu/ before gpu/ in drivers/Makefile and also moves amdkfd/ before radeon/ in drivers/gpu/drm/Makefile.
The rationale is that in general, AMD GPU devices are dependent on AMD IOMMU controller functionality to allow the GPU to access a process's virtual memory address space, without the need for pinning the memory. That's why it makes sense to initialize the iommu/ subsystem ahead of the gpu/ subsystem.
Oded
Oded Gabbay (2):
drivers: Move iommu/ before gpu/ in Makefile
drm: Put amdkfd before radeon in drm Makefile
drivers/Makefile | 6 ++++-- drivers/gpu/drm/Makefile | 2 +- 2 files changed, 5 insertions(+), 3 deletions(-)
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