Re: [RFC PATCH 09/11] drivers: acpi: implement acpi_dma_configure

[Robin Murphy]

Hi Bjorn,

On 15/04/16 17:14, Bjorn Helgaas wrote:
> On Thu, Apr 14, 2016 at 06:25:41PM +0100, Lorenzo Pieralisi wrote:
> > On DT based systems, the of_dma_configure() API implements DMA configuration
> > for a given device. On ACPI systems an API equivalent to of_dma_configure()
> > is missing which implies that it is currently not possible to set-up DMA
> > operations for devices through the ACPI generic kernel layer.
> >
> > This patch fills the gap by introducing acpi_dma_configure/deconfigure()
> > calls, that carry out IOMMU configuration through IORT (on systems where
> > it is present) and call arch_setup_dma_ops(...) with the retrieved
> > parameters.
> >
> > The DMA range size passed to arch_setup_dma_ops() is sized according
> > to the device coherent_dma_mask (starting at address 0x0), mirroring the
> > DT probing path behaviour when a dma-ranges property is not provided
> > for the device being probed; this changes the current arch_setup_dma_ops()
> > call parameters in the ACPI probing case, but since arch_setup_dma_ops()
> > is a NOP on all architectures but ARM/ARM64 this patch does not change
> > the current kernel behaviour on them.
> >
> > This patch updates ACPI and PCI core code to use the newly introduced
> > acpi_dma_configure function, providing the same functionality
> > as of_dma_configure on ARM systems and leaving behaviour unchanged
> > for all other arches.
> >
> > Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@xxxxxxx>
> > Cc: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>
> > Cc: Robin Murphy <robin.murphy@xxxxxxx>
> > Cc: Tomasz Nowicki <tn@xxxxxxxxxxxx>
> > Cc: Joerg Roedel <joro@xxxxxxxxxx>
> > Cc: "Rafael J. Wysocki" <rjw@xxxxxxxxxxxxx>
>
> There's only a tiny PCI change in this series, so I assume somebody
> else will merge all this.  Here's my ack for the PCI part:
>
> Acked-by: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>	# for drivers/pci/probe.c change
>
> One question on use of pci_for_each_dma_alias() below.
>
> > +static int __get_pci_rid(struct pci_dev *pdev, u16 alias, void *data)
> > +{
> > +	u32 *rid = data;
> > +
> > +	*rid = alias;
> > +	return 0;
> > +}
> > +
> > +/**
> > + * iort_iommu_configure - Set-up IOMMU configuration for a device.
> > + *
> > + * @dev: device that requires IOMMU set-up
> > + *
> > + * Returns: iommu_ops pointer on configuration success
> > + *          NULL on configuration failure
> > + */
> > +struct iommu_ops *iort_iommu_configure(struct device *dev)
> > +{
> > +	struct acpi_iort_node *node, *parent;
> > +	struct iommu_ops *ops = NULL;
> > +	struct iommu_fwspec fwspec;
> > +	struct iort_iommu_node *iommu_node;
> > +	u32 rid = 0, devid = 0;
> > +
> > +	if (dev_is_pci(dev)) {
> > +		struct pci_bus *bus = to_pci_dev(dev)->bus;
> > +
> > +		pci_for_each_dma_alias(to_pci_dev(dev), __get_pci_rid,
> > +				       &rid);
>
> You end up with only the last DMA alias in "rid".  Is it really true
> that you only need to call iort_dev_map_rid() for one of the aliases?

Indeed - all we care about is what things look like by the time they 
come out of the root complex on their way to the the IOMMU, so whatever 
intermediate aliasing _within_ the PCI bus might happen along the way 
doesn't actually matter.

Robin.

> > +		node = iort_scan_node(ACPI_IORT_NODE_PCI_ROOT_COMPLEX,
> > +				      iort_find_dev_callback, &bus->dev);
> > +	} else
> > +		node = iort_scan_node(ACPI_IORT_NODE_NAMED_COMPONENT,
> > +				      iort_find_dev_callback, dev);
> > +
> > +	if (!node)
> > +		return NULL;
> > +
> > +	iort_dev_map_rid(node, rid, &devid, ACPI_IORT_NODE_SMMU);
> > +
> > +	parent = iort_find_parent_node(node, ACPI_IORT_NODE_SMMU);
> > +
> > +	if (!parent)
> > +		return NULL;
> > +
> > +	iommu_node = iort_iommu_get_node(parent);
> > +	ops = iommu_node->ops;
> > +
> > +	fwspec.fwnode = iommu_node->fwnode;
> > +	fwspec.param_count = 1;
> > +	fwspec.param[0] = devid;
> > +
> > +	if (!ops || !ops->fw_xlate || ops->fw_xlate(dev, &fwspec))
> > +		return NULL;
> > +
> > +	return ops;
> > +}
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