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Subject: Re: [Linux-fbdev-devel] Re: atyfb in 2.5.51
From: Antonino Daplas <adaplas@pol.net>
To: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@samba.org>,
       Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
       Linux Fbdev development list 
	<linux-fbdev-devel@lists.sourceforge.net>,
       James Simmons <jsimmons@infradead.org>
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On Wed, 2002-12-11 at 04:11, Benjamin Herrenschmidt wrote:
> 
> I don't know if happened with earlier fbdev versions for you, but one
> possibility is that X reconfigures the display base, and possibly more
> bits of the card's internal memory map. Either fbdev should restore
> that, or adapt to what X set. On R128's and radeon's, this is things
> like DISPLAY_BASE_ADDR.
>  
Although this is in the faqs for a long time, (behavior is undefined if
fbdev is used with software that touches the video card) this is an
issue that needs to be taken into consideration.  Without the set_var()
hook, fbcon will depend on the contents of info->var if there is a need
to touch the hardware or not.  And switching from X to the console will
not change the var, but since X actually did touch the hardware, you
just messed up your screen or worse, crashed the hardware.

Before, most drivers just unconditionally refresh the hardware at every
switch  during set_var(). I've been pointing this out for a long time
now, do we unconditionally do a check_var()/set_par() after every
console switch, or do we rely on fbdev and X cooperating with each
other? Or better, maybe fbcon has a way of knowing if the switch came
from  Xfree86.

Tony

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