linux-kernel - Re: [PATCH] drm/i915/psr: simplify enable

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Message-ID: <20181221195318.GA6483@google.com>
Date:   Fri, 21 Dec 2018 12:53:18 -0700
From:   Ross Zwisler <zwisler@...gle.com>
To:     Dhinakaran Pandiyan <dhinakaran.pandiyan@...el.com>
Cc:     linux-kernel@...r.kernel.org, Daniel Vetter <daniel@...ll.ch>,
        David Airlie <airlied@...ux.ie>,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
        Rodrigo Vivi <rodrigo.vivi@...el.com>,
        dri-devel@...ts.freedesktop.org, intel-gfx@...ts.freedesktop.org,
        Jon Flatley <jflat@...gle.com>
Subject: Re: [PATCH] drm/i915/psr: simplify enable_psr handling

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.