Re: [Intel-gfx] [PATCH] drm/i915/guc/slpc: Allow SLPC to use efficient frequency

["Dixit, Ashutosh" <ashutosh.dixit@intel.com>]

On Sun, 14 Aug 2022 16:46:54 -0700, Vinay Belgaumkar wrote:
>
> Host Turbo operates at efficient frequency when GT is not idle unless
> the user or workload has forced it to a higher level. Replicate the same
> behavior in SLPC by allowing the algorithm to use efficient frequency.
> We had disabled it during boot due to concerns that it might break
> kernel ABI for min frequency. However, this is not the case since
> SLPC will still abide by the (min,max) range limits.

This change seems to have broken the i915 kernel ABI for min frequency for
DG2. Tvrtko pointed this out here:

https://patchwork.freedesktop.org/patch/512274/?series=110574&rev=3

These bugs are the result of that ABI break:

Bug: https://gitlab.freedesktop.org/drm/intel/-/issues/6806
Bug: https://gitlab.freedesktop.org/drm/intel/-/issues/6786

On DG2 when we set min == max freq, we see the GPU running not at the set
min == max freq but at efficient freq (different from the set freq).

We are still trying to see if the ABI can be salvaged but something is
definitely wrong at present.

Thanks.
--
Ashutosh