Re: [Linux-fbdev-users] How detect Driver/Hardware capabilities

[Antonino D. <ad...@po...>]

On Wed, 2003-02-26 at 02:09, Andrea Mazzoleni wrote:
> How can I detect the capabilities of a FrameBuffer driver and
> video board ?
> 
> I have an application which generates at runtime the required
> modelines. For this pourpuse I need to know exactly which
> capabilities are available in the underline FrameBuffer
> software/hardware.
> 
> For example, I have a GeForge 2 board without hardware INTERLACE
> support. But I haven't found a way to detect this misfeature from
> user level using the FrameBuffer API. The same apply for DOUBLESCAN
> modes, at present the Nvidia driver does not support them, but the
> driver is not reporting this misfeature in any way.
> 
> Essentially I need a API call to probe the capabilities of the active
> Frame Buffer hardware/driver.
> 

Place all your new values in fb_var_screeninfo (test_var) -- set
FB_VSYNC_INTERLACED bit in test_var->vmode.  Call the fb_set_var ioctl
with the FB_ACTIVATE_TEST bit set in test_var->activate.  If it returns
an error one of your settings is wrong.  If it returns without an error,
check if test_var and the var returned by the ioctl call still matches. 
Ie, if the returned var cleared the FB_VSYNC_INTERLACED bit, then the
driver does not support interlaced mode.  Note:  the ioctl will rarely
return an error because drivers can round off values in your test_var to
ones acceptable by the driver.  Also, you have to recheck _all_ fields
in test_var.

Once you get a var that is acceptable and do a set_var again (this time
using FB_ACTIVATE_NOW flag), get fb_fix_screeninfo again, because "fix"
can change.

Yes, this is a lot of work for user applications and more or less you
have to do some (a lot of!) trial and error.

Tony