Re: [PATCH v2 2/3] PCI: Add DMA configuration for virtual platforms

[Bjorn Helgaas <helgaas@kernel.org>]

On Fri, Feb 28, 2020 at 06:25:37PM +0100, Jean-Philippe Brucker wrote:
> Hardware platforms usually describe the IOMMU topology using either
> device-tree pointers or vendor-specific ACPI tables.  For virtual
> platforms that don't provide a device-tree, the virtio-iommu device
> contains a description of the endpoints it manages.  That information
> allows us to probe endpoints after the IOMMU is probed (possibly as late
> as userspace modprobe), provided it is discovered early enough.
> 
> Add a hook to pci_dma_configure(), which returns -EPROBE_DEFER if the
> endpoint is managed by a vIOMMU that will be loaded later, or 0 in any
> other case to avoid disturbing the normal DMA configuration methods.
> When CONFIG_VIRTIO_IOMMU_TOPOLOGY isn't selected, the call to
> virt_dma_configure() is compiled out.
> 
> As long as the information is consistent, platforms can provide both a
> device-tree and a built-in topology, and the IOMMU infrastructure is
> able to deal with multiple DMA configuration methods.
> 
> Signed-off-by: Jean-Philippe Brucker <jean-philippe@linaro.org>

Acked-by: Bjorn Helgaas <bhelgaas@google.com>

> ---
>  drivers/pci/pci-driver.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/drivers/pci/pci-driver.c b/drivers/pci/pci-driver.c
> index 0454ca0e4e3f..69303a814f21 100644
> --- a/drivers/pci/pci-driver.c
> +++ b/drivers/pci/pci-driver.c
> @@ -18,6 +18,7 @@
>  #include <linux/kexec.h>
>  #include <linux/of_device.h>
>  #include <linux/acpi.h>
> +#include <linux/virt_iommu.h>
>  #include "pci.h"
>  #include "pcie/portdrv.h"
>  
> @@ -1602,6 +1603,10 @@ static int pci_dma_configure(struct device *dev)
>  	struct device *bridge;
>  	int ret = 0;
>  
> +	ret = virt_dma_configure(dev);
> +	if (ret)
> +		return ret;
> +
>  	bridge = pci_get_host_bridge_device(to_pci_dev(dev));
>  
>  	if (IS_ENABLED(CONFIG_OF) && bridge->parent &&
> -- 
> 2.25.0
> 
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