linux-kernel - [RFC PATCH v1 2/6] of/device: Don't back devices DMA with IOMMU if that's undesired by driver

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Message-Id: <20180726231624.21084-3-digetx@gmail.com>
Date:   Fri, 27 Jul 2018 02:16:20 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Thierry Reding <thierry.reding@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Mikko Perttunen <cyndis@...si.fi>,
        Rob Herring <robh+dt@...nel.org>,
        Frank Rowand <frowand.list@...il.com>,
        Ben Skeggs <bskeggs@...hat.com>,
        Russell King <linux@...linux.org.uk>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Joerg Roedel <joro@...tes.org>,
        Nicolas Chauvet <kwizart@...il.com>
Cc:     devicetree@...r.kernel.org, nouveau@...ts.freedesktop.org,
        iommu@...ts.linux-foundation.org, dri-devel@...ts.freedesktop.org,
        linux-tegra@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [RFC PATCH v1 2/6] of/device: Don't back devices DMA with IOMMU if that's undesired by driver

Respect device driver requirement for device DMA not to be implicitly
backed with IOMMU by skipping the backing setup for drivers that do not
want that.

Signed-off-by: Dmitry Osipenko <digetx@...il.com>
---
 drivers/of/device.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/of/device.c b/drivers/of/device.c
index 33d85511d790..e70b7a886875 100644
--- a/drivers/of/device.c
+++ b/drivers/of/device.c
@@ -163,6 +163,13 @@ int of_dma_configure(struct device *dev, struct device_node *np, bool force_dma)
 	dev_dbg(dev, "device is%sbehind an iommu\n",
 		iommu ? " " : " not ");
 
+	/*
+	 * Respect device driver requirement for device DMA not to be
+	 * implicitly backed with IOMMU.
+	 */
+	if (iommu && dev->driver->no_implicit_iommu)
+		iommu = NULL;
+
 	arch_setup_dma_ops(dev, dma_addr, size, iommu, coherent);
 
 	return 0;
-- 
2.18.0