linux-kernel - [PATCH] Reduce extraneous PCI posting reads during Intel AGP initialization

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Date:	Mon, 13 Oct 2008 23:40:11 -0700
From:	Keith Packard <keithp@...thp.com>
To:	linux-kernel <linux-kernel@...r.kernel.org>,
	Intel graphics drivers <Intel-gfx@...ts.freedesktop.org>,
	Dave Airlie <airlied@...ux.ie>
Cc:	keithp@...thp.com
Subject: [PATCH] Reduce extraneous PCI posting reads during Intel AGP
	initialization

From b4ca8f9596e3d5d2a4c090eaf5e4f373c131a476 Mon Sep 17 00:00:00 2001
From: Keith Packard <keithp@...thp.com>
Date: Mon, 13 Oct 2008 23:33:21 -0700
Subject: [PATCH] Reduce extraneous PCI posting reads during Intel AGP initialization

Instead of doing a posting read after each GTT entry update, do a single one
at the end of the writes. This should reduce boot time a tiny amount by
avoiding a lot of extra uncached reads.

Signed-off-by: Keith Packard <keithp@...thp.com>
---
 drivers/char/agp/intel-agp.c |    6 +++---
 1 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/char/agp/intel-agp.c b/drivers/char/agp/intel-agp.c
index 016fdf0..a6a0c34 100644
--- a/drivers/char/agp/intel-agp.c
+++ b/drivers/char/agp/intel-agp.c
@@ -214,8 +214,8 @@ static int intel_i810_configure(void)
 	if (agp_bridge->driver->needs_scratch_page) {
 		for (i = 0; i < current_size->num_entries; i++) {
 			writel(agp_bridge->scratch_page, intel_private.registers+I810_PTE_BASE+(i*4));
-			readl(intel_private.registers+I810_PTE_BASE+(i*4));	/* PCI posting. */
 		}
+		readl(intel_private.registers+I810_PTE_BASE+((i-1)*4));	/* PCI posting. */
 	}
 	global_cache_flush();
 	return 0;
@@ -773,8 +773,8 @@ static int intel_i830_configure(void)
 	if (agp_bridge->driver->needs_scratch_page) {
 		for (i = intel_private.gtt_entries; i < current_size->num_entries; i++) {
 			writel(agp_bridge->scratch_page, intel_private.registers+I810_PTE_BASE+(i*4));
-			readl(intel_private.registers+I810_PTE_BASE+(i*4));	/* PCI Posting. */
 		}
+		readl(intel_private.registers+I810_PTE_BASE+((i-1)*4));	/* PCI Posting. */
 	}
 
 	global_cache_flush();
@@ -989,8 +989,8 @@ static int intel_i915_configure(void)
 	if (agp_bridge->driver->needs_scratch_page) {
 		for (i = intel_private.gtt_entries; i < current_size->num_entries; i++) {
 			writel(agp_bridge->scratch_page, intel_private.gtt+i);
-			readl(intel_private.gtt+i);	/* PCI Posting. */
 		}
+		readl(intel_private.gtt+i-1);	/* PCI Posting. */
 	}
 
 	global_cache_flush();
-- 
1.5.6.5


-- 
keith.packard@...el.com

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