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

From: "Ville Syrjälä" <ville.syrjala@linux.intel.com>
To: Russell King - ARM Linux <linux@arm.linux.org.uk>
Cc: "Thomas Hellstrom" <thellstrom@vmware.com>,
	"Alison Wang" <alison.wang@freescale.com>,
	"Tomi Valkeinen" <tomi.valkeinen@ti.com>,
	dri-devel@lists.freedesktop.org,
	"Laurent Pinchart" <laurent.pinchart@ideasonboard.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>,
	"Ben Skeggs" <bskeggs@redhat.com>
Subject: Re: [PATCH 09/16] drm/irq: Use unsigned int pipe in public API
Date: Thu, 24 Sep 2015 23:20:54 +0300	[thread overview]
Message-ID: <20150924202054.GI26517@intel.com> (raw)
In-Reply-To: <20150924192153.GD21513@n2100.arm.linux.org.uk>

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.

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.

-- 
Ville Syrjälä
Intel OTC
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