linux-kernel - [PATCH v2 1/6] ARM/dma-mapping: Remove iommu_detach

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Date:   Fri, 17 Feb 2023 17:47:31 +0800
From:   Lu Baolu <baolu.lu@...ux.intel.com>
To:     iommu@...ts.linux.dev
Cc:     Joerg Roedel <joro@...tes.org>, Jason Gunthorpe <jgg@...dia.com>,
        Christoph Hellwig <hch@...radead.org>,
        Kevin Tian <kevin.tian@...el.com>,
        Will Deacon <will@...nel.org>,
        Robin Murphy <robin.murphy@....com>,
        linux-kernel@...r.kernel.org, Lu Baolu <baolu.lu@...ux.intel.com>
Subject: [PATCH v2 1/6] ARM/dma-mapping: Remove iommu_detach_device()

iommu_detach_device() attaches the default domain to the device, or if
default domain is not supported by the IOMMU driver, it calls its
set_platform_dma_ops callback. If the default domain is supported or
the IOMMU driver is not iommu-dma aware, iommu_detach_device() is
actually a noop.

The 64-bit ARM drivers always support default domain and iommu-dma is
even not enabled for 32-bit ARM. This turns out that iommu_detach_device()
is always a noop in arm_iommu_detach_device(). Remove it to avoid dead
code.

The bonus is that it also removes a obstacle of arm_iommu_detach_device()
re-entering the iommu core during release_device. With this removed, the
iommu core code could be simplified a lot.

Signed-off-by: Lu Baolu <baolu.lu@...ux.intel.com>
---
 arch/arm/mm/dma-mapping.c | 1 -
 1 file changed, 1 deletion(-)

diff --git a/arch/arm/mm/dma-mapping.c b/arch/arm/mm/dma-mapping.c
index 8bc01071474a..dcbc2f4586d4 100644
--- a/arch/arm/mm/dma-mapping.c
+++ b/arch/arm/mm/dma-mapping.c
@@ -1699,7 +1699,6 @@ void arm_iommu_detach_device(struct device *dev)
 		return;
 	}

-	iommu_detach_device(mapping->domain, dev);
 	kref_put(&mapping->kref, release_iommu_mapping);
 	to_dma_iommu_mapping(dev) = NULL;
 	set_dma_ops(dev, NULL);
-- 
2.34.1