Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932421AbcLIIE6 (ORCPT ); Fri, 9 Dec 2016 03:04:58 -0500 Received: from mail-io0-f195.google.com ([209.85.223.195]:34369 "EHLO mail-io0-f195.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752337AbcLIIE5 (ORCPT ); Fri, 9 Dec 2016 03:04:57 -0500 MIME-Version: 1.0 In-Reply-To: References: <1479888193-23908-1-git-send-email-tomi.valkeinen@ti.com> <1481158879.26959.41.camel@kernel.crashing.org> <20161208101005.6ufl3d4qvwprosju@phenom.ffwll.local> <1481232519.26959.49.camel@kernel.crashing.org> From: Geert Uytterhoeven Date: Fri, 9 Dec 2016 09:04:55 +0100 X-Google-Sender-Auth: J9YFQnm9DZX-Y1luWydz7clLGlU Message-ID: Subject: Re: [RFC PATCH 0/3] staging: remove fbdev drivers To: Dave Airlie Cc: Benjamin Herrenschmidt , Daniel Vetter , Thomas Petazzoni , Linux Fbdev development list , Teddy Wang , Greg Kroah-Hartman , LKML , dri-devel , Tomi Valkeinen , Sudip Mukherjee , Arnaud Patard Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2566 Lines: 55 Hi Dave, On Fri, Dec 9, 2016 at 1:08 AM, Dave Airlie wrote: > On 9 December 2016 at 07:28, Benjamin Herrenschmidt > wrote: >> On Thu, 2016-12-08 at 11:10 +0100, Daniel Vetter wrote: >>> > With drmfb you basically have to shadow everything into memory & copy >>> > over everything, and locks you out of simple 2D accel. For a simple text >>> > console the result is orders of magnitude slower and memory hungry than >>> > a simple fbdev. >>> >>> Not true, we have full fbdev emulation, and drivers can implement the 2d >>> accel in there. And a bunch of them do. It's just that most teams decided >>> that this is pointless waste of their time.j >> >> Ok so my knowledge might be outdated here. I was complaining to Dave about >> how cirrusdrmfb didn't even use blits for fbcon scrolling and always double >> buffered everything, and Dave made the point that you basically had to do >> that for security reasons that I mostly forgot the details of. >> >> It looks like bochsdrmfb and astdrmfb are the same. If things have changed, >> then cool. Can you point me to a drmfb driver that is a good (and not too >> complex) example with simple 2d accel ? I'm thinking mostly of color >> expansion, bitblt and solid fill for fbcon, the way I used to do it in >> radeonfb for example. > > What are people using fbcon for that needs acceleration, this is where I get > a bit lost. > > It's a console, if you aren't sshing into the machine. > > It's main purpose should just be for gathering oopses and you've a lot better > chance of getting an oops if you don't have some sketchy gpu accel in the way. Unless you're using the console as a text console, and don't run e.g. X on top. > The acceleration that most of the 2D things provide isn't ever that > great, and shadowing is a lot more effective if done properly. It's a feature > that kernel ppl obsess over but I don't get a lot of real world feedback, > (booting 9000 scsi nodes with debug on takes a long time was possibly > something I heard once, and I think we resolved). It all depends on the complex balance between GPU performance, CPU performance, CPU-to-frame buffer bandwidth, and amount of available system RAM. Gr{oetje,eeting}s, Geert -- Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org In personal conversations with technical people, I call myself a hacker. But when I'm talking to journalists I just say "programmer" or something like that. -- Linus Torvalds