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

[Summers, Stuart]

On Thu, 2019-05-16 at 18:42 +0300, Jani Nikula wrote:
> On Thu, 16 May 2019, "Summers, Stuart" <stuart.summers at intel.com>
> wrote:
> > On Thu, 2019-05-16 at 12:59 +0300, Jani Nikula wrote:
> > > On Tue, 14 May 2019, Rodrigo Vivi <rodrigo.vivi at intel.com> wrote:
> > > > 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)
> > > 
> > > Please don't conflate alpha_support or force_probe with
> > > *anything*
> > > else.
> > > 
> > > > 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. :/
> > > 
> > > The problem is, if it works with rc6 disabled, it doesn't prove
> > > it's
> > > an
> > > rc6 bug either.
> > 
> > Good point. I'm not saying we should enforce a process of disabling
> > RC6
> > for the platform if enable_rc6=0 results in success. I'm just
> > saying
> > having the option is useful from a debug perspective. We will still
> > need to do the appropriate full analysis, including the normal code
> > review process on a pre-case basis when debug involves this
> > parameter.
> > But the parameter itself is still useful.
> 
> The trouble starts when users figure out that enable_rc6=0 works
> around
> a particular problem they have (likely by way of disabling runtime
> pm,
> not directly related to rc6). You could argue this is a good thing,
> but
> unfortunately we generally never hear from them again, and the root
> cause remains unsolved, with degraded user experience wrt power
> management.

So I understand the reasoning here, and agree that isn't an ideal
situation. I'd also like a way to debug more efficiently. What did you
think about the suggestion from Tvrtko to only apply on
CONFIG_DRM_I915_DEBUG?

Or we could even wrap this entirely with a CONFIG_I915_DEBUG_PM -
although I'd like to suggest we still use the module parameter, we
could just use the config option to hide the modparam under normal
operation.

Thanks,
Stuart

> 
> BR,
> Jani.
> 
> 
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