Re: [PATCH 09/16] drm/irq: Use unsigned int pipe in public API

From: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
To: "Ville Syrjälä" <ville.syrjala@linux.intel.com>
Cc: "Thomas Hellstrom" <thellstrom@vmware.com>,
	"Russell King - ARM Linux" <linux@arm.linux.org.uk>,
	"Alison Wang" <alison.wang@freescale.com>,
	"Tomi Valkeinen" <tomi.valkeinen@ti.com>,
	dri-devel@lists.freedesktop.org,
	"Ben Skeggs" <bskeggs@redhat.com>,
	"Benjamin Gaignard" <benjamin.gaignard@linaro.org>,
	"Alex Deucher" <alexander.deucher@amd.com>,
	"Daniel Vetter" <daniel.vetter@intel.com>,
	"Christian König" <christian.koenig@amd.com>
Subject: Re: [PATCH 09/16] drm/irq: Use unsigned int pipe in public API
Date: Fri, 25 Sep 2015 10:39:29 +0300	[thread overview]
Message-ID: <2104454.nd0EqFqh7d@avalon> (raw)
In-Reply-To: <20150924202054.GI26517@intel.com>

On Thursday 24 September 2015 23:20:54 Ville Syrjälä wrote:
> On Thu, Sep 24, 2015 at 08:21:53PM +0100, Russell King - ARM Linux wrote:
> > On Thu, Sep 24, 2015 at 06:35:31PM +0200, Thierry Reding wrote:
> > > This continues the pattern started in commit cc1ef118fc09 ("drm/irq:
> > > Make pipe unsigned and name consistent"). This is applied to the public
> > > APIs and driver callbacks, so pretty much all drivers need to be updated
> > > to match the new prototypes.
> > 
> > I don't like being forced to use the "pipe" naming in all drivers; I
> > found that really confusing when I first looked at DRM, and it took
> > a long time to work out that "pipe" basically means "crtc" or "gpu".
> 
> crtc mean "cathode ray tube controller". If you weren't used to it,
> it would be pretty much impossible to guess what piece of modern
> hardware that means. So I think it's more a case of "a lot of this
> junk used to be in what people called the crtc, so we'll call
> this modern thing a crtc too". Although I think most of the
> hardware people moved on from using that name quite a long time ago.
> 
> "gpu" can mean either just the part that does the rendering and
> whatnot, or it can mean the entire graphics "card". But calling
> a display pipeline a "gpu" is not done. Now _that_ would be
> confusing.
> 
> "pipe" is fairly nice term, meaning "pipeline". That describes the
> thing quite nicely. Stuff comes in from one end, flows through the
> pipe, and goes out the other end.

To be pedantic the object we call CRTC today is a subset of the pipeline, not 
the full pipeline. Given that the full pipelines can more complex than a 
single chain (think about one CRTC cloned on two encoders and two connectors), 
I can see why the "pipe" name could sound confusing.

> At least both Intel and OMAP used the term pipe or pipeline in the
> hardware docs. Can't really say aything about other brands, at least
> if I discount the more ancient junk I'm familiar with.
> 
> > What's wrong with keeping "crtc" as the index terminology for crtc
> > things?  Surely that's more descriptive of what's going on here?
> 
> I can't speak for Thierry, but I assume the real motivation for this
> renaming was to make it clear which is the "index", and which is the
> crtc object. "pipe" for one, "crtc" for the other. Avoids having
> to call the object "dcrtc", "drm_crtc" or something else entirely.
> And since the object is called "crtc" everywhere else, it's nice not
> to have to make an exception in the vblank code.

-- 
Regards,

Laurent Pinchart

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