Hmm, I don't know how this can be fixed... The problem is that previous to the 
second patch, vgacon does not have a resize method, which basically means that 
vgacon does not care about the dimensions of the terminal, so it accepts all 
modes, illegal or not.  However, with the addition of the vgacon_resize method, 
vgacon will only accept values <= to the original mode size of the vga hardware, 
which is usually 80x25.

Can you try to comment out this lines in drivers/video/console/vgacon.c:
vgacon_resize()?

	if (width % 2 || width > ORIG_VIDEO_COLS ||
	    height > (ORIG_VIDEO_LINES * vga_default_font_height)/
	    c->vc_font.height)
		return -EINVAL;

Begin forwarded message:

Date: Fri, 14 Oct 2005 05:08:31 -0700
From: bugme-daemon@kernel-bugs.osdl.org
To: bugme-new@lists.osdl.org
Subject: [Bugme-new] [Bug 5441] New: SVGATextMode problem on 2.6.14-rc4


http://bugzilla.kernel.org/show_bug.cgi?id=5441

           Summary: SVGATextMode problem on 2.6.14-rc4
    Kernel Version: 2.6.14-rc4
            Status: NEW
          Severity: blocking
             Owner: jsimmons@infradead.org
         Submitter: olel@ans.pl


Most recent kernel where this bug did not occur: 2.6.13.4

Distribution: Slackware

Problem Description:

After upgrding my kernel to 2.6.14-rc4 I noticed that SVGATextMode, instead of
changing screen resolution to 100x40, messed my console completely. 

Reverting those two patches helps:
http://www.kernel.org/git/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commitdiff;h=6d36ba629e0ef47a03d3703ee1d38143c25532a8;hp=7b6a186d65589901a73d460070504a5e02703c45
http://www.kernel.org/git/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commitdiff;h=28254d439b8c65f93cb331f5aa741efa6a8ec62f;hp=ff55fe2075e3901db4dbdc00e0b44a71bef97afd

Steps to reproduce:
Use SVGATextMode to change screen resolution.

Tested on:
 - Matrox Graphics, Inc. MGA G200 AGP

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Hi,

Hum, I didn't know about messy programs like svgatextmode... Couldn't this be integrated in some linux/drivers/video/console/svgacon.c ?... So because of the existence of the svgatextmode program, the kernel is not supposed to touch to CRT_OVERFLOW/SYNC_END/DISP/DISP_END/OFFSET ?

Disabling the check in vgacon_resize() might help indeed, but I'm really not sure whether it will work for any chipset: in my patch, CRT registers are set at each console switch, since stty rows/cols apply to consoles separately...

A solution could be to keep the test, but if it fails, we might assume that the caller knows what it does (i.e. it is svgatextmode) and then disable any further call to vgacon_doresize. Svgatextmode is usually used to _expand_ the display, not to shrink it. And it is harmless in the case of a too big stty rows/cols: the display will just be cropped, hence the user knows that it didn't work and can then revert back.

A better solution would be that svgatextmode explicitely tells the kernel not to care about video timing, but for this an interface needs be defined and svgatextmode be patched.

Created attachment 6303 [details]
Something like this (I tested it on my laptop, it works fine)

Samuel Thibault <samuel.thibault@ens-lyon.org> wrote:
>
> Hum, I didn't know about messy programs like svgatextmode... Couldn't
> this be integrated in some linux/drivers/video/console/svgacon.c ?... So
> because of the existence of the svgatextmode program, the kernel is not
> supposed to touch to CRT_OVERFLOW/SYNC_END/DISP/DISP_END/OFFSET ?
> 
> Disabling the check in vgacon_resize() might help indeed, but I'm really
> not sure whether it will work for any chipset: in my patch, CRT
> registers are set at each console switch, since stty rows/cols apply to
> consoles separately...
> 
> The attached solution is to keep the test, but if it fails, we assume
> that the caller knows what it does (i.e. it is svgatextmode) and then
> disable any further call to vgacon_doresize. Svgatextmode is usually
> used to _expand_ the display, not to shrink it. And it is harmless in
> the case of a too big stty rows/cols: the display will just be cropped.
> I tested it on my laptop, and it works fine with svgatextmode.
> 
> A better solution would be that svgatextmode explicitely tells the
> kernel not to care about video timing, but for this an interface needs
> be defined and svgatextmode be patched.

hm, you removed bugzilla from the Cc.  Please don't do that.  I've restored
it, and I've cc'ed the reporter (Krzysztof) directly.

Krzysztof, could you please test Samuel's fix (which I forwarded) and let
us know?

Thanks.

On Fri, 14 Oct 2005, Andrew Morton wrote:

> Samuel Thibault <samuel.thibault@ens-lyon.org> wrote:
>>
>> Hum, I didn't know about messy programs like svgatextmode... Couldn't
>> this be integrated in some linux/drivers/video/console/svgacon.c ?... So
>> because of the existence of the svgatextmode program, the kernel is not
>> supposed to touch to CRT_OVERFLOW/SYNC_END/DISP/DISP_END/OFFSET ?
>>
>> Disabling the check in vgacon_resize() might help indeed, but I'm really
>> not sure whether it will work for any chipset: in my patch, CRT
>> registers are set at each console switch, since stty rows/cols apply to
>> consoles separately...
>>
>> The attached solution is to keep the test, but if it fails, we assume
>> that the caller knows what it does (i.e. it is svgatextmode) and then
>> disable any further call to vgacon_doresize. Svgatextmode is usually
>> used to _expand_ the display, not to shrink it. And it is harmless in
>> the case of a too big stty rows/cols: the display will just be cropped.
>> I tested it on my laptop, and it works fine with svgatextmode.
>>
>> A better solution would be that svgatextmode explicitely tells the
>> kernel not to care about video timing, but for this an interface needs
>> be defined and svgatextmode be patched.
>
> hm, you removed bugzilla from the Cc.  Please don't do that.  I've restored
> it, and I've cc'ed the reporter (Krzysztof) directly.
>
> Krzysztof, could you please test Samuel's fix (which I forwarded) and let
> us know?

Tested. Both "stty cols 66", when switching from plain 80x25, and 
SVGATextMode work.

Thank you.

Best regards,

 				Krzysztof Ol

Thanks for the report and test.