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Commit 0f97da83 authored by Christian König's avatar Christian König Committed by Bjorn Helgaas
Browse files

PCI/P2PDMA: Allow P2P DMA between any devices under AMD ZEN Root Complex 

The PCI specs say that peer-to-peer DMA should be supported between any two
devices that have a common upstream PCI-to-PCI bridge.  But devices under
different Root Ports don't share a common upstream bridge, and PCIe r4.0,
sec 1.3.1, says routing peer-to-peer transactions between Root Ports in the
same Root Complex is optional.

Many Root Complexes, including AMD ZEN, *do* support peer-to-peer DMA even
between Root Ports.  Add a whitelist and allow peer-to-peer DMA if both
participants are attached to a Root Complex known to support it.

Link: https://lore.kernel.org/linux-pci/20190418115859.2394-1-christian.koenig@amd.com


Signed-off-by: default avatarChristian König <christian.koenig@amd.com>
[bhelgaas: changelog]
Signed-off-by: default avatarBjorn Helgaas <bhelgaas@google.com>
Reviewed-by: default avatarLogan Gunthorpe <logang@deltatee.com>
parent 9e98c678

drivers/pci/p2pdma.c

+35 −3
Original line number Diff line number Diff line
@@ -274,6 +274,30 @@ static void seq_buf_print_bus_devfn(struct seq_buf *buf, struct pci_dev *pdev) 
	seq_buf_printf(buf, "%s;", pci_name(pdev));

}



/*

 * If we can't find a common upstream bridge take a look at the root

 * complex and compare it to a whitelist of known good hardware.

 */

static bool root_complex_whitelist(struct pci_dev *dev)

{

	struct pci_host_bridge *host = pci_find_host_bridge(dev->bus);

	struct pci_dev *root = pci_get_slot(host->bus, PCI_DEVFN(0, 0));

	unsigned short vendor, device;



	if (!root)

		return false;



	vendor = root->vendor;

	device = root->device;

	pci_dev_put(root);



	/* AMD ZEN host bridges can do peer to peer */

	if (vendor == PCI_VENDOR_ID_AMD && device == 0x1450)

		return true;



	return false;

}



/*

 * Find the distance through the nearest common upstream bridge between

 * two PCI devices.
@@ -317,13 +341,13 @@ static void seq_buf_print_bus_devfn(struct seq_buf *buf, struct pci_dev *pdev) 
 * In this case, a list of all infringing bridge addresses will be

 * populated in acs_list (assuming it's non-null) for printk purposes.

 */

static int upstream_bridge_distance(struct pci_dev *a,

				    struct pci_dev *b,

static int upstream_bridge_distance(struct pci_dev *provider,

				    struct pci_dev *client,

				    struct seq_buf *acs_list)

{

	struct pci_dev *a = provider, *b = client, *bb;

	int dist_a = 0;

	int dist_b = 0;

	struct pci_dev *bb = NULL;

	int acs_cnt = 0;



	/*
@@ -354,6 +378,14 @@ static int upstream_bridge_distance(struct pci_dev *a, 
		dist_a++;

	}



	/*

	 * Allow the connection if both devices are on a whitelisted root

	 * complex, but add an arbitary large value to the distance.

	 */

	if (root_complex_whitelist(provider) &&

	    root_complex_whitelist(client))

		return 0x1000 + dist_a + dist_b;



	return -1;



check_b_path_acs: