tree 486845448c30ac78338e471cea2e831dba5127ce
parent ef6239e0cf5e665e7b20fd659678b98331b3081d
author Lucas Stach <dev@lynxeye.de> 1477344724 +0200
committer Alex Deucher <alexander.deucher@amd.com> 1477418242 -0400

drm/radeon: drop register readback in cayman_cp_int_cntl_setup

The read is taking a considerable amount of time (about 50us on this
machine). The register does not ever hold anything other than the ring
ID that is updated in this exact function, so there is no need for
the read modify write cycle.

This chops off a big chunk of the time spent in hardirq disabled
context, as this function is called multiple times in the interrupt
handler. With this change applied radeon won't show up in the list
of the worst IRQ latency offenders anymore, where it was a regular
before.

Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Lucas Stach <dev@lynxeye.de>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org