From: Andi Kleen <ak@suse.de>
Date: Sat, 25 Mar 2006 15:29:37 +0000 (+0100)
Subject: [PATCH] x86_64: Use cpu_relax in poll loop in GART IOMMU
X-Git-Url: https://git.stricted.de/?a=commitdiff_plain;h=85f9eebccde51e24896f31383f5b70776362e1a6;p=GitHub%2FLineageOS%2FG12%2Fandroid_kernel_amlogic_linux-4.9.git

[PATCH] x86_64: Use cpu_relax in poll loop in GART IOMMU

The code waits for the GART to clear the TLB flush bit. Use cpu_relax
in this time to allow hypervisors to yield the CPU in this time.

Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
---

diff --git a/arch/x86_64/kernel/pci-gart.c b/arch/x86_64/kernel/pci-gart.c
index 0c3f052ba6ce..ebd125e968be 100644
--- a/arch/x86_64/kernel/pci-gart.c
+++ b/arch/x86_64/kernel/pci-gart.c
@@ -148,9 +148,12 @@ static void flush_gart(struct device *dev)
 			if (!northbridges[i])
 				continue;
 			/* Make sure the hardware actually executed the flush. */
-			do { 
+			for (;;) { 
 				pci_read_config_dword(northbridges[i], 0x9c, &w);
-			} while (w & 1);
+				if (!(w & 1))
+					break;
+				cpu_relax();
+			}
 		} 
 		if (!flushed) 
 			printk("nothing to flush?\n");