# \[PATCH v8 4/9\] video: fbdev: gxt4500: use pci\_ioremap\_wc\_bar() for framebuffer

- From: Luis R. Rodriguez \<hidden\>
- Date: 2015-06-25 01:33:34 
- List: linux-fbdev
- Page: https://ratatoskr.run/linux-fbdev/2015/06/4522448
- Thread: https://ratatoskr.run/linux-pci/2015/06/4522444/t.md

```text
From: "Luis R. Rodriguez" <redacted>

The driver doesn't use mtrr_add() or arch_phys_wc_add() but
since we know the framebuffer is isolated already on an
ioremap() we can take advantage of write combining for
performance where possible.

In this case there are a few motivations for this:

a) Take advantage of PAT when available

b) Help with the goal of eventually using _PAGE_CACHE_UC over
   _PAGE_CACHE_UC_MINUS on x86 on ioremap_nocache() (see commit
   de33c442e titled "x86 PAT: fix performance drop for glx,
   use UC minus for ioremap(), ioremap_nocache() and
   pci_mmap_page_range()")

Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Cc: Rob Clark <redacted>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Suresh Siddha <redacted>
Cc: Ingo Molnar <redacted>
Cc: Thomas Gleixner <redacted>
Cc: Juergen Gross <jgross@suse.com>
Cc: Daniel Vetter <redacted>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Dave Airlie <airlied@redhat.com>
Cc: Antonino Daplas <adaplas@gmail.com>
Cc: Jean-Christophe Plagniol-Villard <redacted>
Cc: Tomi Valkeinen <redacted>
Cc: <redacted>
Cc: <redacted>
Acked-by: Tomi Valkeinen <redacted>
Signed-off-by: Luis R. Rodriguez <redacted>
---
 drivers/video/fbdev/gxt4500.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/video/fbdev/gxt4500.c b/drivers/video/fbdev/gxt4500.c
index 135d78a..f19133a 100644
--- a/drivers/video/fbdev/gxt4500.c
+++ b/drivers/video/fbdev/gxt4500.c
@@ -662,7 +662,7 @@ static int gxt4500_probe(struct pci_dev *pdev, const struct pci_device_id *ent)
 
 	info->fix.smem_start = fb_phys;
 	info->fix.smem_len = pci_resource_len(pdev, 1);
-	info->screen_base = pci_ioremap_bar(pdev, 1);
+	info->screen_base = pci_ioremap_wc_bar(pdev, 1);
 	if (!info->screen_base) {
 		dev_err(&pdev->dev, "gxt4500: cannot map framebuffer\n");
 		goto err_unmap_regs;
-- 
2.3.2.209.gd67f9d5.dirty

```