5 files changed, 44 insertions, 1 deletions
diff --git a/sys/src/9/pc/fns.h b/sys/src/9/pc/fns.h
index 69c4fc01c..14c30ef21 100644
--- a/sys/src/9/pc/fns.h
+++ b/sys/src/9/pc/fns.h
@@ -123,6 +123,7 @@ void	outss(int, void*, int);
 void	outl(int, ulong);
 void	outsl(int, void*, int);
 ulong	paddr(void*);
+void	patwc(void*, int);
 ulong	pcibarsize(Pcidev*, int);
 void	pcibussize(Pcidev*, ulong*, ulong*);
 int	pcicfgr8(Pcidev*, int);
diff --git a/sys/src/9/pc/mmu.c b/sys/src/9/pc/mmu.c
index b48155084..d97c9a5b5 100644
--- a/sys/src/9/pc/mmu.c
+++ b/sys/src/9/pc/mmu.c
@@ -1065,3 +1065,7 @@ cankaddr(ulong pa)
 	return -KZERO - pa;
 }
 
+void
+patwc(void *, int)
+{
+}
diff --git a/sys/src/9/pc/screen.c b/sys/src/9/pc/screen.c
index c74d2da71..69018c4fe 100644
--- a/sys/src/9/pc/screen.c
+++ b/sys/src/9/pc/screen.c
@@ -492,6 +492,9 @@ vgalinearaddr0(VGAscr *scr, ulong paddr, int size)
 	scr->vaddr = vmap(npaddr, nsize);
 	if(scr->vaddr == 0)
 		return "cannot allocate vga frame buffer";
+
+	patwc(scr->vaddr, nsize);
+
 	scr->vaddr = (char*)scr->vaddr+x;
 	scr->paddr = paddr;
 	scr->apsize = nsize;
diff --git a/sys/src/9/pc64/fns.h b/sys/src/9/pc64/fns.h
index 4b55e7399..41e3380ec 100644
--- a/sys/src/9/pc64/fns.h
+++ b/sys/src/9/pc64/fns.h
@@ -117,6 +117,7 @@ void	outss(int, void*, int);
 void	outl(int, ulong);
 void	outsl(int, void*, int);
 uintptr	paddr(void*);
+void	patwc(void*, int);
 ulong	pcibarsize(Pcidev*, int);
 void	pcibussize(Pcidev*, ulong*, ulong*);
 int	pcicfgr8(Pcidev*, int);
diff --git a/sys/src/9/pc64/mmu.c b/sys/src/9/pc64/mmu.c
index 18b8878f7..ffd077e31 100644
--- a/sys/src/9/pc64/mmu.c
+++ b/sys/src/9/pc64/mmu.c
@@ -31,13 +31,16 @@ static struct {
 	ulong	nfree;
 } mmupool;
 
-/* level */
 enum {
+	/* level */
 	PML4E	= 2,
 	PDPE	= 1,
 	PDE	= 0,
 
 	MAPBITS	= 8*sizeof(m->mmumap[0]),
+
+	/* PAT entry used for write combining */
+	PATWC	= 7,
 };
 
 static void
@@ -130,6 +133,12 @@ mmuinit(void)
 
 	/* SYSCALL flags mask */
 	wrmsr(0xc0000084, 0x200);
+
+	/* IA32_PAT write combining */
+	rdmsr(0x277, &v);
+	v &= ~(255LL<<(PATWC*8));
+	v |= 1LL<<(PATWC*8);	/* WC */
+	wrmsr(0x277, v);
 }
 
 /*
@@ -535,3 +544,28 @@ vunmap(void *v, int)
 {
 	paddr(v);	/* will panic on error */
 }
+
+/*
+ * mark pages as write combining (used for framebuffer)
+ */
+void
+patwc(void *v, int n)
+{
+	uintptr *pte, mask, attr, va;
+	int z, l;
+
+	/* set the bits for all pages in range */
+	for(va = (uintptr)v; n > 0; n -= z, va += z){
+		l = 0;
+		pte = mmuwalk(m->pml4, va, l, 0);
+		if(pte == 0)
+			pte = mmuwalk(m->pml4, va, ++l, 0);
+		if(pte == 0 || (*pte & PTEVALID) == 0)
+			panic("patwc: va=%#p", va);
+		z = PGLSZ(l);
+		z -= va & (z-1);
+		mask = l == 0 ? 3<<3 | 1<<7 : 3<<3 | 1<<12;
+		attr = (((PATWC&3)<<3) | ((PATWC&4)<<5) | ((PATWC&4)<<10));
+		*pte = (*pte & ~mask) | (attr & mask);
+	}
+}