[Intel-gfx] [RFC 8/8] drm/i915: Support for retrieving MMIO register values alongwith timestamps through perf

[Chris Wilson]

On Wed, Aug 05, 2015 at 11:25:44AM +0530, sourab.gupta at intel.com wrote:
> From: Sourab Gupta <sourab.gupta at intel.com>
> 
> This patch adds support for retrieving MMIO register values alongwith
> timestamps and forwarding them to userspace through perf.
> The userspace can request upto 8 MMIO register values to be dumped.
> The addresses of upto 8 MMIO registers can be passed through perf attr
> config. The registers are checked against a whitelist before passing them
> on. The commands to dump the values of these MMIO registers are then
> inserted into the ring alongwith commands to dump the timestamps.

The values reported to userspace are deltas across batches right? We
don't expose the global value to an unprivileged user? It would be nice
to clarify that in perf_init so that the reviewer is aware that
the issue of unprivileged information leak is addressed (or at least
reminded that the register values do not leak!).
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre