[Intel-gfx] [PATCH 1/2] drm/i915: Re-add enable_rc6 modparam

[Summers, Stuart]

On Wed, 2019-05-15 at 06:43 +0100, Tvrtko Ursulin wrote:
> On 15/05/2019 01:06, Rodrigo Vivi wrote:
> > On Tue, May 14, 2019 at 06:32:01PM +0000, Summers, Stuart wrote:
> > > On Tue, 2019-05-14 at 17:53 +0100, Chris Wilson wrote:
> > > > Quoting Stuart Summers (2019-05-14 17:46:52)
> > > > > To allow easier debug of platforms which do not fully support
> > > > > power-saving render C-state 6, add back the module parameter
> > > > > to allow RC6 flows to be disabled. Instead of directly
> > > > > affecting
> > > > > the RC6 states via a bitmask as done previously, use this
> > > > > module
> > > > > parameter to clear the has_rc6 field for these platforms.
> > > > 
> > > > If you know which platforms don't support rc6, don't enable
> > > > rc6.
> > > 
> > > I'd really prefer to have this parameter in place for debug
> > > purposes.
> > > It seems more useful to allow quick testing by reloading i915
> > > than by
> > > requiring a rebuild.
> > > 
> > > Of course, once debug is complete and the platform is known to
> > > either
> > > not support the feature or has some cripling bug around this, I
> > > agree,
> > > rc6 shouldn't be enabled on that platform and i915 should be
> > > updated.
> > 
> > Exactly. We need the flexibility for debug that.
> > unfortunately using debugfs doesn't look a solution.
> > 
> > One possibility that just came to my mind now is, what if we make
> > this only for platforms that are still protected by
> > is_alpha_support=1
> > (soon becoming require_force_probe=1)
> > 
> > But this is just one side of the coin... when product is out there
> > and we want the user to debug the issue to see if it is a RC6 bug
> > we have no way to verify that. :/
> > 
> > Please let's add this back one way or another.
> 
> To throw a compromise option out there - add the modparam for debug 
> builds only (CONFIG_DRM_I915_DEBUG)?

No issues here, and makes sense. If we have concensus, I'd be happy to
add this and repost.

-Stuart

> 
> Regards,
> 
> Tvrtko
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