Re: [Linux-fbdev-devel] [PATCH] Tile Blitting

[Michel <mi...@da...>]

On Don, 2003-02-27 at 15:15, Antonino Daplas wrote: 
> On Thu, 2003-02-27 at 09:18, James Simmons wrote:
>  
> > > Thus, the restriction that the buffer must be completely copied by the
> > > driver before returning.  And because of this restriction, an extra copy
> > > which might be unnecessary cannot be avoided (this was noted by Petr).
> > > 
> > > Treating the buffer as a ringbuffer, we eliminate these restrictions.
> > 
> > I didn't realize that the below was a ringbuffer implementation. The name
> > threw me off. 
> 
> Well, it's not strictly a ringbuffer implementation.  This would require
> a head and tail pointer where fbcon will adjust the tail and the
> driver/hardware will adjust the head.  This will be very difficult to
> implement in a device independent manner.  So we just cheat by issuing
> an fb_sync() per loop to flush all pending commands.

That still seems suboptimal though. What the DRM often does is have the
chip write an age value to a scratch register when it's done processing
something. Maybe something like that could be used to avoid waiting for
the chip to go idle at all?


-- 
Earthling Michel Dänzer (MrCooper)/ Debian GNU/Linux (powerpc) developer
XFree86 and DRI project member   /  CS student, Free Software enthusiast