linux-kernel - [PATCH] x86, aperture: Check for GART before accessing GART registers

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Date:	Wed, 1 Apr 2015 09:32:08 -0500
From:	Aravind Gopalakrishnan <Aravind.Gopalakrishnan@....com>
To:	<tglx@...utronix.de>, <mingo@...hat.com>, <hpa@...or.com>,
	<x86@...nel.org>, <bp@...e.de>, <bhelgaas@...gle.com>,
	<linux-kernel@...r.kernel.org>
CC:	<Suravee.Suthikulpanit@....com>, <joro@...tes.org>,
	Aravind Gopalakrishnan <Aravind.Gopalakrishnan@....com>
Subject: [PATCH] x86, aperture: Check for GART before accessing GART registers

GART registers are not present in newer processors (Fam15h, Model 10h
and later). So, avoid accesses to GART registers in PCI config
space by returning early in early_gart_iommu_check() and
gart_iommu_hole_init() if GART is not available.

Refactoring the family check used in amd_nb into an inline function
so we can use it here as well as in amd_nb.c

Tested the patch on Fam10h and Fam15h Model 00h-fh and this code
runs fine. On Fam15h Model 60h-6fh and on Fam16h, we bail early
as they don't have GART.

Signed-off-by: Aravind Gopalakrishnan <Aravind.Gopalakrishnan@....com>
Reviewed-by: Suravee Suthikulpanit <Suravee.Suthikulpanit@....com>
---
 arch/x86/include/asm/amd_nb.h | 11 +++++++++++
 arch/x86/kernel/amd_nb.c      |  4 +---
 arch/x86/kernel/aperture_64.c |  4 ++--
 3 files changed, 14 insertions(+), 5 deletions(-)

diff --git a/arch/x86/include/asm/amd_nb.h b/arch/x86/include/asm/amd_nb.h
index aaac3b2..864c8bd 100644
--- a/arch/x86/include/asm/amd_nb.h
+++ b/arch/x86/include/asm/amd_nb.h
@@ -98,11 +98,22 @@ static inline u16 amd_get_node_id(struct pci_dev *pdev)
 	return 0;
 }
 
+static inline bool amd_gart_present(void)
+{
+	/* GART present only on Fam15h upto model 0fh */
+	if (boot_cpu_data.x86 == 0xf || boot_cpu_data.x86 == 0x10 ||
+	    (boot_cpu_data.x86 == 0x15 && boot_cpu_data.x86_model < 0x10))
+		return true;
+
+	return false;
+}
+
 #else
 
 #define amd_nb_num(x)		0
 #define amd_nb_has_feature(x)	false
 #define node_to_amd_nb(x)	NULL
+#define amd_gart_present(x)	false
 
 #endif
 
diff --git a/arch/x86/kernel/amd_nb.c b/arch/x86/kernel/amd_nb.c
index 5caed1d..29fa475 100644
--- a/arch/x86/kernel/amd_nb.c
+++ b/arch/x86/kernel/amd_nb.c
@@ -89,9 +89,7 @@ int amd_cache_northbridges(void)
 			next_northbridge(link, amd_nb_link_ids);
 	}
 
-	/* GART present only on Fam15h upto model 0fh */
-	if (boot_cpu_data.x86 == 0xf || boot_cpu_data.x86 == 0x10 ||
-	    (boot_cpu_data.x86 == 0x15 && boot_cpu_data.x86_model < 0x10))
+	if (amd_gart_present())
 		amd_northbridges.flags |= AMD_NB_GART;
 
 	/*
diff --git a/arch/x86/kernel/aperture_64.c b/arch/x86/kernel/aperture_64.c
index 76164e1..1cb170b 100644
--- a/arch/x86/kernel/aperture_64.c
+++ b/arch/x86/kernel/aperture_64.c
@@ -262,7 +262,7 @@ void __init early_gart_iommu_check(void)
 	u64 aper_base = 0, last_aper_base = 0;
 	int aper_enabled = 0, last_aper_enabled = 0, last_valid = 0;
 
-	if (!early_pci_allowed())
+	if (!early_pci_allowed() || !amd_gart_present())
 		return;
 
 	/* This is mostly duplicate of iommu_hole_init */
@@ -356,7 +356,7 @@ int __init gart_iommu_hole_init(void)
 	int i, node;
 
 	if (gart_iommu_aperture_disabled || !fix_aperture ||
-	    !early_pci_allowed())
+	    !early_pci_allowed() || !amd_gart_present())
 		return -ENODEV;
 
 	pr_info("Checking aperture...\n");
-- 
1.9.1

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