linux-kernel - Re: BUG caused by "Use new drm_fb

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Message-ID: <20160209134422.00e6f6b6@lxorguk.ukuu.org.uk>
Date:	Tue, 9 Feb 2016 13:44:22 +0000
From:	One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>
To:	Daniel Vetter <daniel@...ll.ch>
Cc:	Michel Dänzer <michel@...nzer.net>,
	Peter Hurley <peter@...leysoftware.com>,
	Archit Taneja <architt@...eaurora.org>,
	Daniel Vetter <daniel.vetter@...ll.ch>,
	Ben Skeggs <bskeggs@...hat.com>,
	Linux kernel <linux-kernel@...r.kernel.org>,
	"dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>
Subject: Re: BUG caused by "Use new drm_fb_helper functions" series

> > > But a better look has me wondering how all these gpus are syncing
> > > the framebuffer for direct access via cfb_imageblit and friends. I only see
> > > nouveau and intel gma even trying.  
> > 
> > Probably no other DRM driver uses hardware acceleration for fbcon.  
> 
> Yup. We've had patches for i915, resulted in half of mesa+glamour in-kernel, which
> is just pointless.
> -Daniel

When I did the gma500 driver I played with it a little and the only thing
that made any difference was scrolling acceleratin - which actually the
i915 can probably also do without using the 2D/3D engine.

It's actually trying to fix the wrong problem. The real problem is that
the fbcon layer when running pure text output tries to write everything to
the screen rather than just updating the offscreen array of text and
then doing at most one difference update per vblank based upon the state
of the display. That would make most of the dumb fbs feel lightning fast.

Alan