8f9420184a
Space reservation is already safe with respect to the ring->size modulus, but hardware only expects to see values in the range 0...ring->size-1 (inclusive) and so requires the modulus to prevent us writing the value ring->size instead of 0. As this is only required for the register itself, we can defer the modulus to the register update and not perform it after every command packet. We keep the intel_ring_advance() around in the code to provide demarcation for the end-of-packet (which then can be compared against intel_ring_begin() as the number of dwords emitted must match the reserved space). v2: Assert that the ring size is a power-of-two to match assumptions in the code. Simplify the comment before writing the tail value to explain why the modulus is necessary. Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com> Cc: Dave Gordon <david.s.gordon@intel.com> Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/1470174640-18242-13-git-send-email-chris@chris-wilson.co.uk |
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