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=-5.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,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 A62CFC433E9 for ; Thu, 14 Jan 2021 16:12:08 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 6F79A23B2F for ; Thu, 14 Jan 2021 16:12:08 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727438AbhANQMG (ORCPT ); Thu, 14 Jan 2021 11:12:06 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:58852 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725950AbhANQMG (ORCPT ); Thu, 14 Jan 2021 11:12:06 -0500 Received: from mail-ot1-x32c.google.com (mail-ot1-x32c.google.com [IPv6:2607:f8b0:4864:20::32c]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id CD0CCC061757 for ; Thu, 14 Jan 2021 08:11:19 -0800 (PST) Received: by mail-ot1-x32c.google.com with SMTP id o11so5646790ote.4 for ; Thu, 14 Jan 2021 08:11:19 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=ffwll.ch; s=google; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=lI7DNB9PJvzlL1ZP9cY7fdOx2/ptLeVjeZhhrDDi7c4=; b=Zi8S4ocJOhLeZPI7DA82w2n/RGNymWj4EnipZ421KIVCN3q+pn6FHQlQjVv4fbVCTq Arl+l+jzarPBMM/Q4vO6TR9DcPVhQMO9VvuyqHQXyLCv+FfsVMoypWDiVtBzddb+YuxA K1x1YV7KyaUREwbkOGl2QJAf+Oot3y9DhjTh0= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=lI7DNB9PJvzlL1ZP9cY7fdOx2/ptLeVjeZhhrDDi7c4=; b=a+WSZvcXfMAIjyoZOs4t/O1yi8z2mSxIY9bB0kcfSeBwIn+p59zr1ggYR1W6qd2XfN xCUhgFywVX4Nktn/VFVosJAnBUf043SApaD9GBwrWFD5PIANE86xLQVPmqIS2QFnb8gy 3GS/YSJ+jMNn5afvTnQOh4zS/J7yJutoS8pqEeTZLNEeb/8rY29SYOpDNb0yXR6sqt7j 4mKVhSv0RrtZUZXhxD+qfxnbCahCFwhYuW++bQ9YsNJhIEsXIlHSaXwkoROEzNoiO2Vr ljQXOD3Wq+xIb1ktb3ssbIVTgkOlgg7ciPUEEgXPnTYNk3wVSlQF7Q9PtlMNg6MwEmMD 8k+Q== X-Gm-Message-State: AOAM531gCS8qaE2AbZolTl64b9obSBdExaSeV6IqMzm2MxmndcjcpyvI Vod0muK0crHfBVvfYx/OUNWms2yYObzrCImAV0JW8A== X-Google-Smtp-Source: ABdhPJzzz22o9OQD7ab1kI0cLaSVhXvWLJ9AS4BVjPKCWnUBdp3at3x0E09pBUvROlXehDbVAiUAp+GHsISnTag0oIg= X-Received: by 2002:a05:6830:1bef:: with SMTP id k15mr4945559otb.303.1610640679142; Thu, 14 Jan 2021 08:11:19 -0800 (PST) MIME-Version: 1.0 References: <20200916205434.GA10389@duo.ucw.cz> <87czyf5jjp.fsf@vps.thesusis.net> In-Reply-To: From: Daniel Vetter Date: Thu, 14 Jan 2021 17:11:07 +0100 Message-ID: Subject: Re: fbcon: remove soft scrollback code (missing Doc. patch) To: Geert Uytterhoeven Cc: Linus Torvalds , Phillip Susi , Pavel Machek , Randy Dunlap , LKML , "linux-doc@vger.kernel.org" , Greg Kroah-Hartman , dri-devel , Linux Fbdev development list Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jan 14, 2021 at 4:56 PM Geert Uytterhoeven wrote: > > Hi Daniel, > > CC linux-fbdev > > On Tue, Jan 12, 2021 at 5:00 PM Daniel Vetter wrote: > > On Sat, Jan 9, 2021 at 12:11 AM Linus Torvalds > > wrote: > > > On Fri, Jan 8, 2021 at 11:13 AM Phillip Susi wrote: > > > > > Could we pause this madness? Scrollback is still useful. I needed it > > > > > today... it was too small, so command results I was looking for > > > > > already scrolled away, but... life will be really painful with 0 > > > > > scrollback. > > > > > > > > > You'll need it, too... as soon as you get oops and will want to see > > > > > errors just prior to that oops. > > > > > > > > > If it means I get to maintain it... I'm not happy about it but that's > > > > > better than no scrollback. > > > > > > > > Amen! What self respecting admin installs a gui on servers? What do we > > > > have to do to get this back in? What was so buggy with this code that > > > > it needed to be removed? Why was it such a burden to just leave it be? > > > > > > It really was buggy, with security implications. And we have no maintainers. > > > > > > So the scroll-back code can't come back until we have a maintainer and > > > a cleaner and simpler implementation. > > > > > > And no, maintaining it really doesn't mean "just get it back to the > > > old broken state". > > > > > > So far I haven't actually seen any patches, which means that it's not > > > coming back. > > > > > > The good news? If you have an actual text VGA console, that should > > > still work just fine. > > IIRC, all of this was written for systems lacking VGA text consoles > in the first place... > > > Also on anything that is remotely modern (i.e. runs a drm kernel > > modesetting driver undearneath the fbdev/fbcon stack) there's a pile > > more issues on top of just the scrollback/fbcon code being a mess. > > Would it help to remove DRM_FBDEV_EMULATION (instead)? It's a problem with the hardware. "Write some registers and done" isn't how display blocks work nowadays. So your proposal amounts to "no fbdev/fbcon for anything modern-ish". Also I said "a pile more", most of the issues in fbcon/fbdev code apply for all drivers. > > Specifically the locking is somewhere between yolo and outright > > deadlocks. This holds even more so if the use case here is "I want > > scrollback for an oops". There's rough sketches for how it could be > > solved, but it's all very tricky work. > > When an oops happens, all bets are off. At that point, all information > you can extract from the system is valuable, and additional locking > issues are moot. Except the first oops then scrolls aways because it's getting buried under further fail. Your locking needs to be minimally good enough to not make the situation worse. -Daniel > > Also adding dri-devel since defacto that's the only place where > > display people hang out nowadays. > > Please keep on CCing linux-fbdev, especially for patches removing > fbdev features. > > Thanks! > > 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 -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch 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=-3.6 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,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 5D6DEC433E0 for ; Thu, 14 Jan 2021 16:11:22 +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 C7666239EB for ; Thu, 14 Jan 2021 16:11:21 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org C7666239EB Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=ffwll.ch 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 3E48D6E027; Thu, 14 Jan 2021 16:11:21 +0000 (UTC) Received: from mail-ot1-x336.google.com (mail-ot1-x336.google.com [IPv6:2607:f8b0:4864:20::336]) by gabe.freedesktop.org (Postfix) with ESMTPS id C5FCC6E027 for ; Thu, 14 Jan 2021 16:11:19 +0000 (UTC) Received: by mail-ot1-x336.google.com with SMTP id i6so5652694otr.2 for ; Thu, 14 Jan 2021 08:11:19 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=ffwll.ch; s=google; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=lI7DNB9PJvzlL1ZP9cY7fdOx2/ptLeVjeZhhrDDi7c4=; b=Zi8S4ocJOhLeZPI7DA82w2n/RGNymWj4EnipZ421KIVCN3q+pn6FHQlQjVv4fbVCTq Arl+l+jzarPBMM/Q4vO6TR9DcPVhQMO9VvuyqHQXyLCv+FfsVMoypWDiVtBzddb+YuxA K1x1YV7KyaUREwbkOGl2QJAf+Oot3y9DhjTh0= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=lI7DNB9PJvzlL1ZP9cY7fdOx2/ptLeVjeZhhrDDi7c4=; b=VKnNFc00a4qOi3R2YjNZ6zYsPYlqxnqCFO/G7F318q4UP8Q1cJnqVfT+Wk2WloQqVy liq04E1lm9HWnwQUm+NAmiqhg6IbpNPLwB5mo0DfPQAZt9eFIkfmcAUkqZw+kADYydxN XtkUGzz6Py06BIJ2Mg7mZ1daNC8D/rkHwOFdzGExgsz26X6XjPcQI0Dhyz3Z5t6NI5P5 kezDP8QuH3x4WT9mwgqS7xa+wV/XND4i/4c/8VpU+EONSJ0rLri+2ML1Ve5twiAiBqT6 bdx5eQFv9zvNY5wOXQkKU6ZsRO+iMTmrikxFsNhoOVI2oSRcj8qnQSuaivggUwEe0AtI vrVA== X-Gm-Message-State: AOAM533G0b7QHLz3r91nwFNLXK6HhOL2wbQy8dysurLpVsXaqFv5vji+ pEM+lJ1gArmrVrJIa7IcuY6Q9QJVsIhLgovF9sHuSQ== X-Google-Smtp-Source: ABdhPJzzz22o9OQD7ab1kI0cLaSVhXvWLJ9AS4BVjPKCWnUBdp3at3x0E09pBUvROlXehDbVAiUAp+GHsISnTag0oIg= X-Received: by 2002:a05:6830:1bef:: with SMTP id k15mr4945559otb.303.1610640679142; Thu, 14 Jan 2021 08:11:19 -0800 (PST) MIME-Version: 1.0 References: <20200916205434.GA10389@duo.ucw.cz> <87czyf5jjp.fsf@vps.thesusis.net> In-Reply-To: From: Daniel Vetter Date: Thu, 14 Jan 2021 17:11:07 +0100 Message-ID: Subject: Re: fbcon: remove soft scrollback code (missing Doc. patch) To: Geert Uytterhoeven 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: Linux Fbdev development list , Phillip Susi , "linux-doc@vger.kernel.org" , Greg Kroah-Hartman , Randy Dunlap , LKML , dri-devel , Pavel Machek , Linus Torvalds Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" On Thu, Jan 14, 2021 at 4:56 PM Geert Uytterhoeven wrote: > > Hi Daniel, > > CC linux-fbdev > > On Tue, Jan 12, 2021 at 5:00 PM Daniel Vetter wrote: > > On Sat, Jan 9, 2021 at 12:11 AM Linus Torvalds > > wrote: > > > On Fri, Jan 8, 2021 at 11:13 AM Phillip Susi wrote: > > > > > Could we pause this madness? Scrollback is still useful. I needed it > > > > > today... it was too small, so command results I was looking for > > > > > already scrolled away, but... life will be really painful with 0 > > > > > scrollback. > > > > > > > > > You'll need it, too... as soon as you get oops and will want to see > > > > > errors just prior to that oops. > > > > > > > > > If it means I get to maintain it... I'm not happy about it but that's > > > > > better than no scrollback. > > > > > > > > Amen! What self respecting admin installs a gui on servers? What do we > > > > have to do to get this back in? What was so buggy with this code that > > > > it needed to be removed? Why was it such a burden to just leave it be? > > > > > > It really was buggy, with security implications. And we have no maintainers. > > > > > > So the scroll-back code can't come back until we have a maintainer and > > > a cleaner and simpler implementation. > > > > > > And no, maintaining it really doesn't mean "just get it back to the > > > old broken state". > > > > > > So far I haven't actually seen any patches, which means that it's not > > > coming back. > > > > > > The good news? If you have an actual text VGA console, that should > > > still work just fine. > > IIRC, all of this was written for systems lacking VGA text consoles > in the first place... > > > Also on anything that is remotely modern (i.e. runs a drm kernel > > modesetting driver undearneath the fbdev/fbcon stack) there's a pile > > more issues on top of just the scrollback/fbcon code being a mess. > > Would it help to remove DRM_FBDEV_EMULATION (instead)? It's a problem with the hardware. "Write some registers and done" isn't how display blocks work nowadays. So your proposal amounts to "no fbdev/fbcon for anything modern-ish". Also I said "a pile more", most of the issues in fbcon/fbdev code apply for all drivers. > > Specifically the locking is somewhere between yolo and outright > > deadlocks. This holds even more so if the use case here is "I want > > scrollback for an oops". There's rough sketches for how it could be > > solved, but it's all very tricky work. > > When an oops happens, all bets are off. At that point, all information > you can extract from the system is valuable, and additional locking > issues are moot. Except the first oops then scrolls aways because it's getting buried under further fail. Your locking needs to be minimally good enough to not make the situation worse. -Daniel > > Also adding dri-devel since defacto that's the only place where > > display people hang out nowadays. > > Please keep on CCing linux-fbdev, especially for patches removing > fbdev features. > > Thanks! > > 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 -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch _______________________________________________ dri-devel mailing list dri-devel@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/dri-devel