linux-kernel - Re: [RFC PATCH 09/11] drivers: acpi: implement acpi_dma

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Date:	Fri, 15 Apr 2016 11:14:00 -0500
From:	Bjorn Helgaas <helgaas@...nel.org>
To:	Lorenzo Pieralisi <lorenzo.pieralisi@....com>
Cc:	iommu@...ts.linux-foundation.org,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Robin Murphy <robin.murphy@....com>,
	Tomasz Nowicki <tn@...ihalf.com>,
	Joerg Roedel <joro@...tes.org>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Will Deacon <will.deacon@....com>,
	Marc Zyngier <marc.zyngier@....com>,
	Hanjun Guo <hanjun.guo@...aro.org>,
	Jon Masters <jcm@...hat.com>,
	Sinan Kaya <okaya@...eaurora.org>, linux-acpi@...r.kernel.org,
	linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [RFC PATCH 09/11] drivers: acpi: implement acpi_dma_configure

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@....com>
> Cc: Bjorn Helgaas <bhelgaas@...gle.com>
> Cc: Robin Murphy <robin.murphy@....com>
> Cc: Tomasz Nowicki <tn@...ihalf.com>
> Cc: Joerg Roedel <joro@...tes.org>
> Cc: "Rafael J. Wysocki" <rjw@...ysocki.net>

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@...gle.com>	# 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?

> +		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;
> +}