From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Antonino A. Daplas" Subject: Re: [PATCH 1/1 2.6.15-rc4-git1] Fix switching to KD_TEXT Date: Fri, 09 Dec 2005 08:24:15 +0800 Message-ID: <4398CEAF.9050303@gmail.com> References: <4398B888.50005@t-online.de> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <4398B888.50005@t-online.de> Sender: linux-kernel-owner@vger.kernel.org List-Id: Cc: linux-kernel@vger.kernel.org, linux-fbdev-devel@lists.sourceforge.net, Andrew Morton Knut Petersen wrote: > Every framebuffer driver relies on the assumption that the set_par() > function > of the driver is called before drawing functions and other functions > dependent > on the hardware state are executed. > > This assumption is false in two cases, and one is a genuine linux > bug: > > 1: Whenever you switch from X to a framebuffer console for the very > first time, there is a chance that a broken X system has _not_ set > the mode to KD_GRAPHICS, thus the vt and framebuffer code > executes a screen redraw and several other functions before a > set_par() is executed. This is believed to be not a bug of linux > but a bug of X/xdm. > > 2: Whenever a switch from X to a framebuffer console occures, > the pan_display() function of the driver is called once before > the set_par() function of the driver is called. Code path: > complete_change_console -> redraw_screen -> fbcon_switch -> > bit_update_start-> fb_pan_display -> xyz_pan_display. > This is clearly a bug of linux. This part, #2, can be easily fixed. > > Although our primary goal must be to fix linux bugs and not to work > around bugs of X, the patch fixes both of the cases. > > The advantage and correctness of this patch should be obvious. Yes, it > does add a possibly slow call to the fb_set_par() function, but at this > point it is necessary. > > Signed-off-by: Knut Petersen Sorry, NAK for now. Unless other people agree that it is okay for them to have an unconditional call to set_par() for every console switch. Note that the set_par() in some drivers is terribly slow (several seconds at least). Let's wait a few days, if nobody disagrees with you, so be it. Tony