[ofa-general] [PATCH] IB/mlx4: Use pgprot_writecombine() for BlueFlame pages

[Roland Dreier]

The PAT work on x86 has finally made pgprot_writecombine() a usable API
for modular drivers.  As the comment indicates, this is exactly what we
want to use in mlx4_ib to map BlueFlame pages up to userspace, since
using WC for these pages improves small message latency significantly.

Signed-off-by: Roland Dreier <rolandd at cisco.com>
---
Could someone test this patch on top of 2.6.29, and see if it provides
the right latency benefit?  If it looks good, I'll send it upstream for
2.6.30.

Thanks,
  Roland

diff --git a/drivers/infiniband/hw/mlx4/main.c b/drivers/infiniband/hw/mlx4/main.c
index 2ccb9d3..ae3d759 100644
--- a/drivers/infiniband/hw/mlx4/main.c
+++ b/drivers/infiniband/hw/mlx4/main.c
@@ -394,8 +394,7 @@ static int mlx4_ib_mmap(struct ib_ucontext *context, struct vm_area_struct *vma)
 				       PAGE_SIZE, vma->vm_page_prot))
 			return -EAGAIN;
 	} else if (vma->vm_pgoff == 1 && dev->dev->caps.bf_reg_size != 0) {
-		/* FIXME want pgprot_writecombine() for BlueFlame pages */
-		vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot);
+		vma->vm_page_prot = pgprot_writecombine(vma->vm_page_prot);
 
 		if (io_remap_pfn_range(vma, vma->vm_start,
 				       to_mucontext(context)->uar.pfn +