• Laurent Pinchart's avatar
    ARM: dma-mapping: Don't tear down third-party mappings · a93a121a
    Laurent Pinchart authored
    arch_setup_dma_ops() is used in device probe code paths to create an
    IOMMU mapping and attach it to the device. The function assumes that the
    device is attached to a device-specific IOMMU instance (or at least a
    device-specific TLB in a shared IOMMU instance) and thus creates a
    separate mapping for every device.
    
    On several systems (Renesas R-Car Gen2 being one of them), that
    assumption is not true, and IOMMU mappings must be shared between
    multiple devices. In those cases the IOMMU driver knows better than the
    generic ARM dma-mapping layer and attaches mapping to devices manually
    with arm_iommu_attach_device(), which sets the DMA ops for the device.
    
    The arch_setup_dma_ops() function takes this into account and bails out
    immediately if the device already has DMA ops assigned. However, the
    corresponding arch_teardown_dma_ops() function, called from driver
    unbind code paths (including probe deferral), will tear the mapping down
    regardless of who created it. When the device is reprobed
    arch_setup_dma_ops() will be called again but won't perform any
    operation as the DMA ops will still be set.
    
    We need to reset the DMA ops in arch_teardown_dma_ops() to fix this.
    However, we can't do so unconditionally, as then a new mapping would be
    created by arch_setup_dma_ops() when the device is reprobed, regardless
    of whether the device needs to share a mapping or not. We must thus keep
    track of whether arch_setup_dma_ops() created the mapping, and only in
    that case tear it down in arch_teardown_dma_ops().
    
    Keep track of that information in the dev_archdata structure. As the
    structure is embedded in all instances of struct device let's not grow
    it, but turn the existing dma_coherent bool field into a bitfield that
    can be used for other purposes.
    
    Fixes: 09515ef5 ("of/acpi: Configure dma operations at probe time for platform/amba/pci bus devices")
    Reviewed-by: default avatarRobin Murphy <robin.murphy@arm.com>
    Signed-off-by: default avatarLaurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
    Signed-off-by: default avatarJoerg Roedel <jroedel@suse.de>
    a93a121a
device.h 771 Bytes