Re: [PATCH] Do set var even if no fb_check_var() provided.

[Helge Deller <deller@gmx.de>]

Geert Uytterhoeven wrote:
> On Wed, 27 Aug 2008, Takashi Yoshii wrote:
>> The behavior of FBIOSET_VSCREENINFO seems to be weired on FB which does
>> not
>>  provides fbops->fb_check_var.
>> It doesn't set anything, but gets info->var instead, and returns no
>> error. It is just same as FBIOGET_VSCREENINFO does.
>> 
>> IMHO, this should be one of the following candidates,
>>  1. set var without check.
>>  2. do nothing but return error (setting var is not supported).
>> or
>>  3. it's a bug (fb_check_var should always be provided).
>> 
>> The patch at the bottom implements "1".
>> 
>> Because I don't know API specification, nor the history of the code,
>> I would like people who knows well to discuss this.
> 
> If the driver doesn't provide a fb_check_var(), it means it cannot
> change video mode. Hence this rules out #1.
> 
> #2 is not acceptable, as it will break existing applications. It's also
> incorrect, as FBIOPUT_VSCREENINFO should succeed for supported modes.
> For unsupported modes, the mode should be rounded up to a supported mode,
> if possible. In the case of drivers that support one fixed mode only, this
> rounding up is relaxed to `rounding' to the sole supported mode.
> 
> #3 is also wrong, as fb_check_var() has been deliberately made optional to
> simplify drivers that support one fixed mode only.
> 
> Conclusion: nothing should be changed?

I'm not sure.
On parisc we just stumbled over exactly this problem where I think Takashi's
proposal "1." is probably the right solution.

Please see my Xorg bugzilla entry:
https://bugs.freedesktop.org/show_bug.cgi?id=17153 
and this problem description/thread ("X won't start with VisEG and
2.6.22.19"):
http://thread.gmane.org/gmane.linux.ports.parisc/564/focus=592

Helge


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