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[directfb-dev] Re: Non-working AGP hack
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[directfb-dev] Re: Non-working AGP hack

Quoting Antonino Daplas (
> On Tue, 2002-06-18 at 13:23, Ville Syrjälä wrote:
> > I tried to glue some AGP stuff to DirectFB and G400 (patch included). So
> > far all it manages to do is hang my system. I'm still able to use the
> > magic sysrq key to reboot with my disks clean. It's supposed to put all
> > video surfaces into AGP memory.
> > 
> > I haven't found any decent docs on the agpgart interface so I'm not sure
> > if what I'm doing is correct. Currently I allocate 64MB of AGP memory but
> > I adjust the heap offset to 32MB so only the upper half of that gets used.
> > This way I can check if the buffer is in card memory or AGP memory. Card <
> > 32MB, AGP >= 32MB. 
> > 
> I haven't read the code thoroughly nor tested the patch since I don't
> have a matrox card.  But from what I can see, the agp bind offset is at
> 32MB, and then you tell the driver that the framebuffer pointer is at
> that offset (state->destination->video.offset).  Unfortunately, that
> will not coincide with the framebuffer drivers's internal pointer and
> buffer length (fix->smem_start and fix->smem_len) which is probably at
> offset 0 and size == card vidmem length.  From the point of view of the
> framebuffer driver, the AGP surface is not displayable.  And you will
> get undefined behavior with other operations such as display panning,
> etc.

The primary layer is still located in the video memory and the framebuffer
driver doesn't need to know about the AGP usage at all.

> Probably the AGP surface can be used as a backbuffer from which you can
> write to then later on blit to the frontbuffer.  I doubt flipping will
> work since flips require FB_IOCTL_PANDISPLAY. Ie. it need to have a
> video policy similar to CSP_SYSTEMONLY with the exception that it
> supports hardware blits.

The surfaces in AGP aperture will be offscreen surfaces only.

Best regards,
  Denis Oliver Kropp

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