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

[Rodrigo Vivi <rodrigo.vivi@intel.com>]

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.

Thanks,
Rodrigo.

> 
> Thanks,
> Stuart
> 
> > -Chris



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