linux-kernel - Re: console font limits

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Message-Id: <E0FF8D28-219F-44D5-88B4-BDE6A4D6605A@mac.com>
Date:	Thu, 3 May 2007 20:17:48 -0400
From:	Kyle Moffett <mrmacman_g4@....com>
To:	Jan Engelhardt <jengelh@...ux01.gwdg.de>
Cc:	"H. Peter Anvin" <hpa@...or.com>,
	Geert Uytterhoeven <geert@...ux-m68k.org>,
	Albert Cahalan <acahalan@...il.com>,
	"Antonino A. Daplas" <adaplas@...il.com>,
	linux-kernel <linux-kernel@...r.kernel.org>, aeb@....nl
Subject: Re: console font limits

On May 03, 2007, at 16:16:51, Jan Engelhardt wrote:
> On May 3 2007 13:15, H. Peter Anvin wrote:
>> Jan Engelhardt wrote:
>>>
>>>> Put people didn't like that, and disabled text output when the  
>>>> console is in KD_GRAPHICS mode...
>>>
>>> at the cost of not getting the kernel oops, heh.
>>
>> I thought the reason we didn't display text in KD_GRAPHICS mode  
>> was that KD_GRAPHICS might mean "in a completely different mode  
>> that only userspace knows about."
>
> Hrm. Maybe we need a distinction into KD_KGRAPHICS and KD_UGRAPHICS  
> then.

Actually I think the real problem was that "KD_GRAPHICS" got  
overloaded to mean "some userspace program is probably poking at the  
GPU in very direct ways possibly including /dev/mem".  As such it  
really isn't safe at all for the kernel to write stuff to the screen  
in that situation; you could turn a panic()+reboot-after-30-secs into  
an unrecoverable hard PCI bus lockup.  IIRC there were at least a  
couple chipsets which had that problem with X.  If we can implement  
enough APIs for X to do all of its stuff from userspace without iopl 
() or /dev/mem then we could probably bring back the option for  
dumping oopses to screen in KD_GRAPHICS mode, but otherwise it'll  
just cause more headaches.

Cheers,
Kyle Moffett

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