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        <rfc822;linux-pci@vger.kernel.org>); Thu, 31 Aug 2017 10:21:21 -0400
From: Zhou Wang <wangzhou1@hisilicon.com>
Subject: [Question] PCI ACS is broken for ARM SMMU v3?
To: Alex Williamson <alex.williamson@redhat.com>,
        Will Deacon <will.deacon@arm.com>
CC: <linux-arm-kernel@lists.infradead.org>,
        Linux PCI <linux-pci@vger.kernel.org>,
        <wangzhou1@hisilicon.com>
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Date: Thu, 31 Aug 2017 22:21:00 +0800
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Hi Will and Alex,

pci_request_acs is called in drivers/iommu/arm-smmu-v3.c to set pci_acs_enable.

PCI subsystem tries to enable ACS as below:

	pci_device_add
		--> pci_init_capabilities
			--> pci_enable_acs

in ACPI PCI driver. However, ACPI PCI driver will be called before SMMU v3 driver,
which will lead pci_enable_acs to return directly as pci_acs_enable is not set
before SMMU v3 driver loading.

I think this is a bug, what do you think about this problem?

Best,
Zhou