Re: [Dri-devel] DRM programming help

[Gareth H. <gar...@ac...>]

On Mon, Dec 10, 2001 at 07:29:47PM -0800, vo...@mi... wrote:
> > 
> > I'm not sure but maybe this is related to the AGP aperture size as
> > configured in the BIOS setup?
> 
> I found out what it is, but I do not know yet what to do about it.
> 
> Gareth - could you comment please ?

Sure.

> What happens is that Radeon has its internal view of physical space an
> important part of which is the location of framebuffer - determined by
> MC_FB_LOCATION register. Now it so happens that DRI sets this to start at
> 0. Hence when I try to DMA from the card it thinks that any small physical
> address is a place in video ram and not system memory. So any attempt to
> DMA into pages with small physical addresses fail.
> 
> I have tried resetting MC_FB_LOCATION to it's pci aperture as
> recommended in the documentation. The problem is that at the minimum it
> screws up display - so something else needs to be changed. Additionally I
> get a hard lockup first chance DRI code kicks in.
> 
> Gareth, in radeon_cp.c I see the following code:
> 
> static void radeon_cp_init_ring_buffer( drm_device_t *dev,
> =09=09=09=09        drm_radeon_private_t *dev_priv )
> {
> =09u32 ring_start, cur_read_ptr;
> =09u32 tmp;
> 
> =09/* Initialize the memory controller */
> =09RADEON_WRITE( RADEON_MC_FB_LOCATION,
> =09=09      (dev_priv->agp_vm_start - 1) & 0xffff0000 );
> 
> =09if ( !dev_priv->is_pci ) {
> =09=09RADEON_WRITE( RADEON_MC_AGP_LOCATION,
> =09=09=09      (((dev_priv->agp_vm_start - 1 +
> =09=09=09=09 dev_priv->agp_size) & 0xffff0000) |
> =09=09=09       (dev_priv->agp_vm_start >> 16)) );
> =09}
> 
> 
> How do you know that you will never need to use system ram with small
> physical address ? I have looked at agpgart and it allocates memory with=20
> alloc_page(GFP_KERNEL) and can, in principle, give you any kind of memory.
> 
> Was there any particular reason for this setting ?

I wouldn't know, I didn't write that code and I no longer have access to
Radeon specs.  Perhaps you should talk with Kevin Martin...

-- Gareth