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.