drm/amdkfd: Avoid integer underflow with ffs in EOP ring size calc

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The low 6 bits of cp_hqd_eop_control store the base-2 logarithm
of the EOP ring size. This was calculated as

ffs(q->eop_ring_buffer_size / sizeof(unsigned int)) - 1 - 1

But ffs can in theory return 1 or 0, so this could underflow
(although in practice the ring buffer size cannot be less than 4096).

Change this to

ffs(q->eop_ring_buffer_size / sizeof(unsigned int) / 4)

using properties of logarithms.

Reviewed-by: Kent Russell <kent.russell@amd.com>
Signed-off-by: David Francis <David.Francis@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
(cherry picked from commit 4f18c56630)
Cc: stable@vger.kernel.org

...

This commit is contained in:

David Francis 2026-08-05 09:51:35 -04:00 • committed by Alex Deucher

parent 04de4007d3

commit c883d0a132

4 changed files with 4 additions and 4 deletions

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2

drivers/gpu/drm/amd/amdkfd/kfd_mqd_manager_v10.c

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drivers/gpu/drm/amd/amdkfd/kfd_mqd_manager_v11.c

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drivers/gpu/drm/amd/amdkfd/kfd_mqd_manager_v12.c

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drivers/gpu/drm/amd/amdkfd/kfd_mqd_manager_v12_1.c

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