Re: can't access video memory?

["Antonino A. Daplas" <adaplas@gmail.com>]

Zack Smith wrote:
> Hi all,
> 
> As an experiment I tried accessing a part of (shared) video memory
> on my system that is not being used for display data, and this caused the
> kernel to crash. I have 6 megs of space and the display is using only half,
> but accessing above the 3 meg mark causes the problem. Accessing
> the lower 3 megs works fine.
> 
> Does anyone know what might cause this?

Depends on the driver.  It's possible that the driver did not ioremap
the entire graphics aperture (ie ioremapped only the first 3 megs).  Or
the driver set info->fix.smem_len to only 3 MB instead of 6.

Some drivers are now differentiating between remapped size vs actual
physical size (radeonfb).  info->screen_size, if not zero, tells the
amount of the remapped size while info->fix.smem_len, the actual physical
size.

Tony


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