In agp(4) avoid the need to flush all cpu caches with wbinvd between

updating the GTT and flushing the AGP TLB by storing the GTT in
write-combining memory.

On x86 flushing the AGP TLB is done by an I/O operation or a store to a
MMIO register in uncacheable memory.  Both cases imply that WC buffers are
flushed so no memory barriers are needed.

On powerpc there is no WC memory type.  It maps to uncacheable memory and
two stores to uncacheable memory, such as to the GTT and then to an MMIO
register, are strongly ordered, so no memory barriers are needed either.

MFC after:	1 month

1 files changed, 6 insertions, 7 deletions

diff --git a/sys/dev/agp/agp_i810.c b/sys/dev/agp/agp_i810.c
index dbf34e3..9afd201 100644
--- a/sys/dev/agp/agp_i810.c
+++ b/sys/dev/agp/agp_i810.c
@@ -66,6 +66,8 @@ __FBSDID("$FreeBSD$");
 #include <dev/pci/pci_private.h>
 
 #include <vm/vm.h>
+#include <vm/vm_extern.h>
+#include <vm/vm_kern.h>
 #include <vm/vm_param.h>
 #include <vm/vm_object.h>
 #include <vm/vm_page.h>
@@ -1388,17 +1390,16 @@ agp_i810_install_gatt(device_t dev)
 		sc->dcache_size = 0;
 
 	/* According to the specs the gatt on the i810 must be 64k. */
-	sc->gatt->ag_virtual = contigmalloc(64 * 1024, M_AGP, 0, 0, ~0,
-	    PAGE_SIZE, 0);
+	sc->gatt->ag_virtual = (void *)kmem_alloc_contig(kernel_arena,
+	    64 * 1024, M_NOWAIT | M_ZERO, 0, ~0, PAGE_SIZE,
+	    0, VM_MEMATTR_WRITE_COMBINING);
 	if (sc->gatt->ag_virtual == NULL) {
 		if (bootverbose)
 			device_printf(dev, "contiguous allocation failed\n");
 		return (ENOMEM);
 	}
 
-	bzero(sc->gatt->ag_virtual, sc->gatt->ag_entries * sizeof(u_int32_t));
 	sc->gatt->ag_physical = vtophys((vm_offset_t)sc->gatt->ag_virtual);
-	agp_flush_cache();
 	/* Install the GATT. */
 	bus_write_4(sc->sc_res[0], AGP_I810_PGTBL_CTL,
 	    sc->gatt->ag_physical | 1);
@@ -1497,7 +1498,7 @@ agp_i810_deinstall_gatt(device_t dev)
 
 	sc = device_get_softc(dev);
 	bus_write_4(sc->sc_res[0], AGP_I810_PGTBL_CTL, 0);
-	contigfree(sc->gatt->ag_virtual, 64 * 1024, M_AGP);
+	kmem_free(kernel_arena, (vm_offset_t)sc->gatt->ag_virtual, 64 * 1024);
 }
 
 static void
@@ -2052,7 +2053,6 @@ agp_i810_bind_memory(device_t dev, struct agp_memory *mem, vm_offset_t offset)
 			sc->match->driver->install_gtt_pte(dev, (offset + i) >>
 			    AGP_PAGE_SHIFT, mem->am_physical + i, 0);
 		}
-		agp_flush_cache();
 		mem->am_offset = offset;
 		mem->am_is_bound = 1;
 		mtx_unlock(&sc->agp.as_lock);
@@ -2093,7 +2093,6 @@ agp_i810_unbind_memory(device_t dev, struct agp_memory *mem)
 			sc->match->driver->install_gtt_pte(dev,
 			    (mem->am_offset + i) >> AGP_PAGE_SHIFT, 0, 0);
 		}
-		agp_flush_cache();
 		mem->am_is_bound = 0;
 		mtx_unlock(&sc->agp.as_lock);
 		return (0);