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

[Jani Nikula <jani.nikula@linux.intel.com>]

On Thu, 16 May 2019, "Summers, Stuart" <stuart.summers@intel.com> wrote:
> On Thu, 2019-05-16 at 12:59 +0300, Jani Nikula wrote:
>> On Tue, 14 May 2019, Rodrigo Vivi <rodrigo.vivi@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.

BR,
Jani.


-- 
Jani Nikula, Intel Open Source Graphics Center
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