linux-kernel - [RFC/PATCH 1/9] arm: dma-mapping: Don't override dma_ops in arch_setup_dma

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Date:	Fri, 15 May 2015 02:00:02 +0300
From:	Laurent Pinchart <laurent.pinchart+renesas@...asonboard.com>
To:	linux-kernel@...r.kernel.org
Cc:	linux-arm-kernel@...ts.infradead.org,
	iommu@...ts.linux-foundation.org,
	Laura Abbott <lauraa@...eaurora.org>,
	Arnd Bergmann <arnd@...db.de>,
	Mitchel Humpherys <mitchelh@...eaurora.org>,
	Joreg Roedel <joro@...tes.org>,
	Will Deacon <will.deacon@....com>,
	Grant Likely <grant.likely@...aro.org>,
	Robin Murphy <robin.murphy@....com>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	Thierry Reding <thierry.reding@...il.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: [RFC/PATCH 1/9] arm: dma-mapping: Don't override dma_ops in arch_setup_dma_ops()

The arch_setup_dma_ops() function is in charge of setting dma_ops with a
call to set_dma_ops(). set_dma_ops() is also called from

- highbank and mvebu bus notifiers
- dmabounce (to be replaced with swiotlb)
- arm_iommu_attach_device

(arm_iommu_attach_device is itself called from IOMMU and bus master
device drivers)

To allow the arch_setup_dma_ops() call to be moved from device add time
to device probe time we must ensure that dma_ops already setup by any of
the above callers will not be overriden.

Aftering replacing dmabounce with swiotlb, converting IOMMU drivers to
of_xlate and taking care of highbank and mvebu, the workaround should be
removed.

Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@...asonboard.com>
---
 arch/arm/mm/dma-mapping.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/arch/arm/mm/dma-mapping.c b/arch/arm/mm/dma-mapping.c
index 09c5fe3d30c2..7aa5e339a596 100644
--- a/arch/arm/mm/dma-mapping.c
+++ b/arch/arm/mm/dma-mapping.c
@@ -2117,6 +2117,15 @@ void arch_setup_dma_ops(struct device *dev, u64 dma_base, u64 size,
 	struct dma_map_ops *dma_ops;
 
 	dev->archdata.dma_coherent = coherent;
+
+	/*
+	 * Don't override the dma_ops if they have already been set. Ideally
+	 * this should be the only location where dma_ops are set, remove this
+	 * check when all other callers of set_dma_ops will have disappeared.
+	 */
+	if (dev->archdata.dma_ops)
+		return;
+
 	if (arm_setup_iommu_dma_ops(dev, dma_base, size, iommu))
 		dma_ops = arm_get_iommu_dma_map_ops(coherent);
 	else
-- 
2.3.6

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