linux-kernel - [PATCH] ASPM: Use msleep instead of cpu

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Message-ID: <20081222221156.29645.95982.stgit@bluto>
Date:	Mon, 22 Dec 2008 15:11:57 -0700
From:	Andrew Patterson <andrew.patterson@...com>
To:	linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org
Cc:	andrew.patterson@...com, matthew@....cx, shaohua.li@...el.com
Subject: [PATCH] ASPM: Use msleep instead of cpu_relax during link retraining

ASPM: Use msleep instead of cpu_relax during link retraining

The cpu_relax() function can be a noop on certain architectures
like IA-64 when CPU threads are disabled, so use msleep instead
during link retraining busy/wait loop.

Introduce define LINK_RETRAIN_TIMEOUT instead of hard-coding
timeout in pcie_aspm_configure_common_clock.

Signed-off-by: Andrew Patterson <andrew.patterson@...com>
---

diff --git a/drivers/pci/pcie/aspm.c b/drivers/pci/pcie/aspm.c
index e361c7d..c00fd65 100644
--- a/drivers/pci/pcie/aspm.c
+++ b/drivers/pci/pcie/aspm.c
@@ -17,6 +17,7 @@
 #include <linux/init.h>
 #include <linux/slab.h>
 #include <linux/jiffies.h>
+#include <linux/delay.h>
 #include <linux/pci-aspm.h>
 #include "../pci.h"
 
@@ -70,6 +71,8 @@ static const char *policy_str[] = {
 	[POLICY_POWERSAVE] = "powersave"
 };
 
+#define LINK_RETRAIN_TIMEOUT HZ
+
 static int policy_to_aspm_state(struct pci_dev *pdev)
 {
 	struct pcie_link_state *link_state = pdev->link_state;
@@ -217,16 +220,18 @@ static void pcie_aspm_configure_common_clock(struct pci_dev *pdev)
 	pci_write_config_word(pdev, pos + PCI_EXP_LNKCTL, reg16);
 
 	/* Wait for link training end */
-	/* break out after waiting for 1 second */
+	/* break out after waiting for timeout */
 	start_jiffies = jiffies;
-	while ((jiffies - start_jiffies) < HZ) {
+	for (;;) {
 		pci_read_config_word(pdev, pos + PCI_EXP_LNKSTA, &reg16);
 		if (!(reg16 & PCI_EXP_LNKSTA_LT))
 			break;
-		cpu_relax();
+		if ((jiffies - start_jiffies) >= LINK_RETRAIN_TIMEOUT)
+			break;
+		msleep(1);
 	}
 	/* training failed -> recover */
-	if ((jiffies - start_jiffies) >= HZ) {
+	if ((jiffies - start_jiffies) >= LINK_RETRAIN_TIMEOUT) {
 		dev_printk (KERN_ERR, &pdev->dev, "ASPM: Could not configure"
 			    " common clock\n");
 		i = 0;

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