[rfc] Radeon AGP support patches

[Konstantin Belousov]

On Sun, Oct 26, 2014 at 04:24:42PM +0100, Tijl Coosemans wrote:
> Hi,
> 
> I worked on AGP support for Radeon cards this week.  Please take a look
> at the attached patches.
> 
> Patch 1:
> Adds support for AGP_USER_TYPES to sys/dev/agp.  For normal memory types
> a vm_object is allocated, for user types only a vm_page array.  It is
> then up to the caller (e.g. TTM code) to manage this array.  Arbitrary
> pages can be mapped into the GTT this way.

> Patch 3:
> Enable AGP support in sys/dev/drm2.  In PCI mode the GTT exists on the
> graphics card so when accessing system memory it already does its own
> virtual address translation and only physical addresses appear on the
> system bus.  The CPU can access the same addresses with its own VM
> system like it always does.  In AGP mode, translation is done by the
> AGP chipset so fictitious addresses appear on the system bus.  For the
> CPU cache management to work correctly it needs to use these same
> fictitious addresses instead of using the real physical addresses
> directly.  The patch marks the AGP aperture range fictitious in
> radeon_device.c where the VRAM aperture is also marked fictitious such
> that PHYS_TO_VM_PAGE in ttm_bo_vm_fault works for addresses in this
> range.
> 
> The rest of the patch is mostly porting to our agp_* API.  It also
> fixes two memory leaks in ttm_agp_backend.c.  One is a missing free in
> ttm_agp_tt_create.  The other is because ttm_agp_bind allocates an
> agp_memory struct but ttm_agp_unbind does not free it.  So when calling
> ttm_agp_bind a second time the reference to the struct is lost.  The
> patch changes ttm_agp_bind so the allocation only happens in the first
> call.  The struct is released in ttm_agp_destroy.
Looking at the combination of patch 1 + 3.

Do you really need to change the container for the AGP_USER_MEMORY ?
Wouldn't it be enough to allocate array in ttm_agp_bind() and copy
pointers to pages from the agp backing object to the array ?