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

["Ville Syrjälä" <syrjala@sci.fi>]

On Wed, Aug 27, 2008 at 11:49:15PM +0200, Helge Deller wrote:
> 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.

What about this?

4. Provide a generic check_var() that does some basic sanity checking
against info->var (eg. check xres, yres and bits_per_pixel).

-- 
Ville Syrjälä
syrjala@sci.fi
http://www.sci.fi/~syrjala/

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