Re: [PATCH] drm/i915: Populate pipe_offsets[] & co. accurately

From: "Ville Syrjälä" <ville.syrjala@linux.intel.com>
To: Lucas De Marchi <lucas.demarchi@intel.com>
Cc: intel-gfx@lists.freedesktop.org
Subject: Re: [PATCH] drm/i915: Populate pipe_offsets[] & co. accurately
Date: Wed, 6 Mar 2019 20:01:05 +0200	[thread overview]
Message-ID: <20190306180105.GL3888@intel.com> (raw)
In-Reply-To: <20190306175533.GJ3888@intel.com>

On Wed, Mar 06, 2019 at 07:55:33PM +0200, Ville Syrjälä wrote:
> On Wed, Mar 06, 2019 at 09:42:57AM -0800, Lucas De Marchi wrote:
> > On Wed, Mar 06, 2019 at 05:13:39PM +0200, Ville Syrjälä wrote:
> > >On Wed, Mar 06, 2019 at 02:55:58PM +0000, Chris Wilson wrote:
> > >> Quoting Ville Syrjälä (2019-03-06 14:52:11)
> > >> > On Wed, Mar 06, 2019 at 09:31:48AM +0000, Chris Wilson wrote:
> > >> > > Quoting Ville Syrjala (2019-03-05 19:29:05)
> > >> > > > From: Ville Syrjälä <ville.syrjala@linux.intel.com>
> > >> > > >
> > >> > > > At some point people have started to assume that
> > >> > > > pipe_offsets[] & co. are only populated for pipes and whatnot
> > >> > > > that actually exist. That is in fact not currently true, but
> > >> > > > we can easily make it so.
> > >> > >
> > >> > > Any benefits of knock on effect?
> > >> >
> > >> > What kind of knock on effect we're thinking?
> > >>
> > >> Just wondering why people are eager to make the assumption that
> > >> non-existent pipes are not set. I presume its to make code neater.
> > >>
> > >> i.e. why cater to their whims at all?
> > >
> > >Yeah, I guess this was done just to avoid having convoluted platform
> > >checks all over. I've not checked the code to see if there are
> > >more places where we could simplify the existing code by adopting
> > >this approach.
> > >
> > >However now that you forced me to think a bit I realize that this
> > >may break in the presence of fused off pipes. Not quite sure how
> > >the registers for such fused off blocks would behave. If we aren't
> > >allowed to touch those registers we'd need to move this stuff
> > >into the runtime info. That feels a bit wasteful, so as an
> > >alternative we could just add one or two bitmasks instead.
> > >
> > >Cc:ing Lucas who seems to the main offender here...
> > 
> > humn.. is this about the EDP transcoder? Missing some context here.
> > Did I miss any platform not setting trans_offsets for TRANSCODER_EDP,
> > even if it has? glancing over the possible mistake.... chv? :-/
> 
> Currently .trans_offsets[TRANSCODER_EDP] != 0 on _every_ platform.
> So using that to determine if a transcoder is present is not going
> to work.

So far the HAS_EDP_TRANSCODER() thing is not actually a problem as
it's only called from the ddi code which guarantees that the transcoder
is in fact present. But the error capture code is now very much wrong.

-- 
Ville Syrjälä
Intel
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