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From: Christoph Hellwig <hch@lst.de>
To: Russell King <linux@armlinux.org.uk>
Cc: "Robin Murphy" <robin.murphy@arm.com>,
	linux-arm-kernel@lists.infradead.org, iommu@lists.linux.dev,
	"Marek Behún" <kabel@kernel.org>
Subject: [PATCH 1/2] ARM/dma-mappіng: don't override ->dma_coherent when set from a bus notifier
Date: Thu,  6 Oct 2022 09:48:23 +0200	[thread overview]
Message-ID: <20221006074824.521457-2-hch@lst.de> (raw)
In-Reply-To: <20221006074824.521457-1-hch@lst.de>

Commit ae626eb97376 ("ARM/dma-mapping: use dma-direct unconditionally")
caused a regression on the mvebu platform, wherein devices that are
dma-coherent are marked as dma-noncoherent, because although
mvebu_hwcc_notifier() after that commit still marks then as coherent,
the arm_coherent_dma_ops() function, which is called later, overwrites
this setting, since it is being called from drivers/of/device.c with
coherency parameter determined by of_dma_is_coherent(), and the
device-trees do not declare the 'dma-coherent' property.

Fix this by defaulting never clearing the dma_coherent flag in
arm_coherent_dma_ops().

Fixes: ae626eb97376 ("ARM/dma-mapping: use dma-direct unconditionally")
Reported-by: Marek Behún <kabel@kernel.org>
Tested-by: Marek Behún <kabel@kernel.org>
---
 arch/arm/mm/dma-mapping.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/arch/arm/mm/dma-mapping.c b/arch/arm/mm/dma-mapping.c
index 089c9c644cce2..bfc7476f14114 100644
--- a/arch/arm/mm/dma-mapping.c
+++ b/arch/arm/mm/dma-mapping.c
@@ -1769,8 +1769,16 @@ static void arm_teardown_iommu_dma_ops(struct device *dev) { }
 void arch_setup_dma_ops(struct device *dev, u64 dma_base, u64 size,
 			const struct iommu_ops *iommu, bool coherent)
 {
-	dev->archdata.dma_coherent = coherent;
-	dev->dma_coherent = coherent;
+	/*
+	 * Due to legacy code that sets the ->dma_coherent flag from a bus
+	 * notifier we can't just assign coherent to the ->dma_coherent flag
+	 * here, but instead have to make sure we only set but never clear it
+	 * for now.
+	 */
+	if (coherent) {
+		dev->archdata.dma_coherent = true;
+		dev->dma_coherent = true;
+	}
 
 	/*
 	 * Don't override the dma_ops if they have already been set. Ideally
-- 
2.30.2


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  reply	other threads:[~2022-10-06  7:49 UTC|newest]

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-10-06  7:48 mvebu DMA fix Christoph Hellwig
2022-10-06  7:48 ` Christoph Hellwig [this message]
2022-10-06  7:48 ` [PATCH 2/2] ARM/dma-mapping: remove the dma_coherent member of struct dev_archdata Christoph Hellwig
2022-10-06 11:52 ` mvebu DMA fix Russell King (Oracle)

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