Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753577AbbF2J60 (ORCPT ); Mon, 29 Jun 2015 05:58:26 -0400 Received: from mail-ob0-f169.google.com ([209.85.214.169]:33193 "EHLO mail-ob0-f169.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753477AbbF2J6S (ORCPT ); Mon, 29 Jun 2015 05:58:18 -0400 MIME-Version: 1.0 X-Originating-IP: [212.51.149.109] In-Reply-To: <20150629094215.GD12383@pd.tnic> References: <1435305314-14337-1-git-send-email-rui.y.wang@intel.com> <3908561D78D1C84285E8C5FCA982C28F32AA062A@ORSMSX114.amr.corp.intel.com> <20150627141237.GE26543@pd.tnic> <20150629080914.GB12383@pd.tnic> <20150629094215.GD12383@pd.tnic> Date: Mon, 29 Jun 2015 11:58:17 +0200 Message-ID: Subject: Re: drm/mgag200: doesn't work in panic context From: Daniel Vetter To: Borislav Petkov Cc: "Luck, Tony" , "Wang, Rui Y" , Dave Airlie , "Clark, Rob" , "Roper, Matthew D" , "Chen, Gong" , Linux Kernel Mailing List 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: 1644 Lines: 31 On Mon, Jun 29, 2015 at 11:42 AM, Borislav Petkov wrote: >> drm_fb_helper_panic isn't the only panic handler - fbdev/fbcon have >> their own. They interfere, and fbdev blissfully assumes that it can >> call almost any driver hook from hardirq context. Which means you'd >> also need to consolidate the various hand-rolled (in drivers instead >> of the fbdev helper) bits to offload fbdev callbacks to workers and >> make sure we don't go boom in panics in there either. > > Hmmm, this would mean to go and tell them through the panic notifier > to not do anything "risky" anymore. Perhaps even stop them from doing > regular tasks which could become risky in the case of panic. I guess > this would mean, we should be doing the same in other subsystems too. Not sure that applies to other subsystems, it's really just history. fbdev was designed for a world where register banging and some writes to a gart was all you had to do for graphics, and you can very well do that from hardirq context. And fbdev will take care of some simple locking itself if needed. The problem really is that drm drivers are anything but simple, and there's a bit of room to share more code and tricks (and fix up even more corner-cases) between drm drivers in the shared fbdev emulation library. -Daniel -- Daniel Vetter Software Engineer, Intel Corporation +41 (0) 79 365 57 48 - http://blog.ffwll.ch -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/