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From:   Daniel Vetter <daniel@ffwll.ch>
Date:   Mon, 24 Dec 2018 10:35:09 +0100
Message-ID: <CAKMK7uHhDTNhoGVWECHrHFN8qGTqdtHBL3zZvp2jLeuZnEA-=g@mail.gmail.com>
Subject: Re: [PATCH] drm/i915/psr: simplify enable_psr handling
To:     Ross Zwisler <zwisler@google.com>
Cc:     Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        David Airlie <airlied@linux.ie>,
        Jani Nikula <jani.nikula@linux.intel.com>,
        Joonas Lahtinen <joonas.lahtinen@linux.intel.com>,
        Rodrigo Vivi <rodrigo.vivi@intel.com>,
        dri-devel <dri-devel@lists.freedesktop.org>,
        intel-gfx <intel-gfx@lists.freedesktop.org>,
        Jon Flatley <jflat@google.com>
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On Fri, Dec 21, 2018 at 8:53 PM Ross Zwisler <zwisler@google.com> wrote:
>
> On Fri, Dec 21, 2018 at 11:23:07AM -0800, Dhinakaran Pandiyan wrote:
> > On Fri, 2018-12-21 at 10:23 -0700, Ross Zwisler wrote:
> > > The following commit:
> > >
> > > commit 2bdd045e3a30 ("drm/i915/psr: Check if VBT says PSR can be
> > > enabled.")
> > >
> > > added some code with no usable functionality.  Regardless of how the
> > > psr
> > > default is set up in the BDB_DRIVER_FEATURES section, if the
> > > enable_psr
> > > module parameter isn't specified it defaults to 0.
> > Right, that was intentional and the commit message even makes a note of
> > it
> > " Note: The feature currently remains disabled by default for all
> > platforms irrespective of what VBT says."
> >
> >
> > Anyway, we've enabled the feature by default now and the current code
> > should take into account the VBT flag if the module parameter is left
> > to a default value. Please check git://anongit.freedesktop.org/drm-tip
> > drm-tip.
>
> Fair enough.  It's a bad pattern to introduce dead code as a placeholder for
> some future work, though.  This code has been in the tree for three major
> kernel releases (v4.{18,19,20}) without providing any useful functionality.

Getting PSR enabled by default on at least a few platforms took years.
Insisting that we do not ever merge such code also doesn't work.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch