linux-kernel - [RFC PATCH v2 03/15] arm64: mm: change IOMMU notifier action to attach DMA ops

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Date:	Tue,  7 Jun 2016 14:30:58 +0100
From:	Lorenzo Pieralisi <lorenzo.pieralisi@....com>
To:	iommu@...ts.linux-foundation.org
Cc:	Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
	Will Deacon <will.deacon@....com>,
	Catalin Marinas <catalin.marinas@....com>,
	Robin Murphy <robin.murphy@....com>,
	Marc Zyngier <marc.zyngier@....com>,
	Joerg Roedel <joro@...tes.org>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Tomasz Nowicki <tn@...ihalf.com>,
	Hanjun Guo <hanjun.guo@...aro.org>,
	Jon Masters <jcm@...hat.com>,
	Sinan Kaya <okaya@...eaurora.org>, linux-acpi@...r.kernel.org,
	linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org
Subject: [RFC PATCH v2 03/15] arm64: mm: change IOMMU notifier action to attach DMA ops

Current bus notifier in ARM64 (__iommu_attach_notifier)
attempts to attach dma_ops to a device on BUS_NOTIFY_ADD_DEVICE
action notification.

This causes issues on ACPI based systems, where PCI devices
can be added before the IOMMUs the devices are attached to
had a chance to be probed, causing failures on attempts to
attach dma_ops in that the domain for the respective IOMMU
may not be set-up yet by the time the bus notifier is run.

Devices dma_ops do not require to be set-up till the matching
device drivers are probed. This means that instead of running
the notifier attaching dma_ops to devices (__iommu_attach_notifier)
on BUS_NOTIFY_ADD_DEVICE action, it can be run just before the
device driver is bound to the device in question (on action
BUS_NOTIFY_BIND_DRIVER) so that it is certain that its IOMMU
group and domain are set-up accordingly at the time the
notifier is triggered.

This patch changes the notifier action upon which dma_ops
are attached to devices and defer it to driver binding time,
so that IOMMU devices have a chance to be probed and to register
their bus notifiers before the dma_ops attach sequence for a
device is actually carried out.

Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@....com>
Cc: Will Deacon <will.deacon@....com>
Cc: Catalin Marinas <catalin.marinas@....com>
Cc: Robin Murphy <robin.murphy@....com>
---
 arch/arm64/mm/dma-mapping.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/arm64/mm/dma-mapping.c b/arch/arm64/mm/dma-mapping.c
index c566ec8..79b0882 100644
--- a/arch/arm64/mm/dma-mapping.c
+++ b/arch/arm64/mm/dma-mapping.c
@@ -848,7 +848,7 @@ static int __iommu_attach_notifier(struct notifier_block *nb,
 {
 	struct iommu_dma_notifier_data *master, *tmp;

-	if (action != BUS_NOTIFY_ADD_DEVICE)
+	if (action != BUS_NOTIFY_BIND_DRIVER)
 		return 0;

 	mutex_lock(&iommu_dma_notifier_lock);
-- 
2.6.4