From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-3.7 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 1C90CC388F7 for ; Wed, 28 Oct 2020 16:46:05 +0000 (UTC) Received: from gabe.freedesktop.org (gabe.freedesktop.org [131.252.210.177]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 3FE3A247F1 for ; Wed, 28 Oct 2020 16:46:03 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 3FE3A247F1 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=ravnborg.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=dri-devel-bounces@lists.freedesktop.org Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id 4CB1C6E4D7; Wed, 28 Oct 2020 16:46:01 +0000 (UTC) Received: from asavdk3.altibox.net (asavdk3.altibox.net [109.247.116.14]) by gabe.freedesktop.org (Postfix) with ESMTPS id B6F766E11C; Wed, 28 Oct 2020 16:45:59 +0000 (UTC) Received: from ravnborg.org (unknown [188.228.123.71]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by asavdk3.altibox.net (Postfix) with ESMTPS id 441B920025; Wed, 28 Oct 2020 17:45:54 +0100 (CET) Date: Wed, 28 Oct 2020 17:45:52 +0100 From: Sam Ravnborg To: Daniel Vetter Subject: Re: [PATCH] fbcon: Disable accelerated scrolling Message-ID: <20201028164552.GA546379@ravnborg.org> References: <20201028160600.3752105-1-daniel.vetter@ffwll.ch> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20201028160600.3752105-1-daniel.vetter@ffwll.ch> X-CMAE-Score: 0 X-CMAE-Analysis: v=2.3 cv=VbvZwmh9 c=1 sm=1 tr=0 a=S6zTFyMACwkrwXSdXUNehg==:117 a=S6zTFyMACwkrwXSdXUNehg==:17 a=kj9zAlcOel0A:10 a=7gkXJVJtAAAA:8 a=69Fu8BYl47zMrmpAOGAA:9 a=CjuIK1q_8ugA:10 a=E9Po1WZjFZOl8hwRPBS3:22 X-BeenThere: dri-devel@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Direct Rendering Infrastructure - Development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Bartlomiej Zolnierkiewicz , Tetsuo Handa , Greg Kroah-Hartman , Linus Torvalds , "Gustavo A. R. Silva" , DRI Development , Peilin Ye , George Kennedy , Tomi Valkeinen , Ben Skeggs , nouveau@lists.freedesktop.org, Daniel Vetter , Nathan Chancellor , Jiri Slaby , Peter Rosin Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" Hi Daniel et al. On Wed, Oct 28, 2020 at 05:06:00PM +0100, Daniel Vetter wrote: > So ever since syzbot discovered fbcon, we have solid proof that it's > full of bugs. And often the solution is to just delete code and remove > features, e.g. 50145474f6ef ("fbcon: remove soft scrollback code"). > > Now the problem is that most modern-ish drivers really only treat > fbcon as an dumb kernel console until userspace takes over, and Oops > printer for some emergencies. Looking at drm drivers and the basic > vesa/efi fbdev drivers shows that only 3 drivers support any kind of > acceleration: > > - nouveau, seems to be enabled by default > - omapdrm, when a DMM remapper exists using remapper rewriting for > y/xpanning > - gma500, but that is getting deleted now for the GTT remapper trick, > and the accelerated copyarea never set the FBINFO_HWACCEL_COPYAREA > flag, so unused (and could be deleted already I think). > > No other driver supportes accelerated fbcon. And fbcon is the only > user of this accel code (it's not exposed as uapi through ioctls), > which means we could garbage collect fairly enormous amounts of code > if we kill this. > > Plus because syzbot only runs on virtual hardware, and none of the > drivers for that have acceleration, we'd remove a huge gap in testing. > And there's no other even remotely comprehensive testing aside from > syzbot. > > This patch here just disables the acceleration code by always > redrawing when scrolling. So far I follow you - and agree. Acked-by: Sam Ravnborg > The plan is that once this has been merged > for well over a year in released kernels, we can start to go around > and delete a lot of code. Why wait one year? We deleted the scrollback code without any prior warning - which was fine. And acceleration support has less users so there should be no reason to wait. So unless there are good arguments that I miss then we should just delete the acceleration code outright. Sam _______________________________________________ dri-devel mailing list dri-devel@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/dri-devel