linux-kernel - [PATCH V5 3/4] x86/PCI: Stop enabling ECS for AMD CPUs after Fam16h

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Message-ID: <20140521231817.26447.55150.stgit@bhelgaas-glaptop.roam.corp.google.com>
Date:	Wed, 21 May 2014 17:18:17 -0600
From:	Bjorn Helgaas <bhelgaas@...gle.com>
To:	Suravee Suthikulpanit <Suravee.Suthikulpanit@....com>
Cc:	Robert Richter <rric@...nel.org>,
	Daniel J Blueman <daniel@...ascale.com>,
	Andreas Herrmann <herrmann.der.user@...glemail.com>,
	linux-kernel@...r.kernel.org,
	Aravind Gopalakrishnan <Aravind.Gopalakrishnan@....com>,
	linux-pci@...r.kernel.org, Borislav Petkov <bp@...e.de>,
	Myron Stowe <myron.stowe@...hat.com>
Subject: [PATCH V5 3/4] x86/PCI: Stop enabling ECS for AMD CPUs after Fam16h

ECS is an AMD mechanism that allows access to extended PCI config space
(offsets 256-4096) via I/O ports CF8/CFCh.  We normally use ECAM, i.e.,
MMCONFIG, to access that space, but apparently old machines have issues
that meant we couldn't use ECAM.

The solution was to enable ECS so we could use configuration mechanism #1
(I/O ports CF8/CFCh) to access extended config space.  See 831d991821da
("x86: add PCI extended config space access for AMD Barcelona").

New machines should be able to use ECAM, which means they don't need the
CPU-specific code to enable ECS.  This patch leaves ECS the same on all
existing platforms, but stops enabling it on platforms after Fam16h.

Those future platforms should be able to use the standard ACPI MCFG/_CBA
descriptions of the PCIe ECAM mechanism.

Signed-off-by: Bjorn Helgaas <bhelgaas@...gle.com>
CC: Robert Richter <rric@...nel.org>
---
 arch/x86/pci/amd_bus.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/arch/x86/pci/amd_bus.c b/arch/x86/pci/amd_bus.c
index aa936e3a2019..67dadf179348 100644
--- a/arch/x86/pci/amd_bus.c
+++ b/arch/x86/pci/amd_bus.c
@@ -405,7 +405,9 @@ static int __init amd_postcore_init(void)
 		return 0;

 	early_fill_mp_bus_info();
-	pci_io_ecs_init();
+
+	if (boot_cpu_data.x86 <= 0x16)
+		pci_io_ecs_init();

 	return 0;
 }

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