Commit aaca43fd authored by Logan Gunthorpe's avatar Logan Gunthorpe Committed by Bjorn Helgaas
Browse files

PCI: Add "pci=disable_acs_redir=" parameter for peer-to-peer support 



To support peer-to-peer traffic on a segment of the PCI hierarchy, we must
disable the ACS redirect bits for select PCI bridges.  The bridges must be
selected before the devices are discovered by the kernel and the IOMMU
groups created.  Therefore, add a kernel command line parameter to specify
devices which must have their ACS bits disabled.

The new parameter takes a list of devices separated by a semicolon.  Each
device specified will have its ACS redirect bits disabled.  This is
similar to the existing 'resource_alignment' parameter.

The ACS Request P2P Request Redirect, P2P Completion Redirect and P2P
Egress Control bits are disabled, which is sufficient to always allow
passing P2P traffic uninterrupted.  The bits are set after the kernel
(optionally) enables the ACS bits itself.  It is also done regardless of
whether the kernel or platform firmware sets the bits.

If the user tries to disable the ACS redirect for a device without the ACS
capability, print a warning to dmesg.

Signed-off-by: default avatarLogan Gunthorpe <logang@deltatee.com>
[bhelgaas: reorder to add the generic code first and move the
device-specific quirk to subsequent patches]
Signed-off-by: default avatarBjorn Helgaas <bhelgaas@google.com>
Reviewed-by: default avatarStephen Bates <sbates@raithlin.com>
Reviewed-by: default avatarAlex Williamson <alex.williamson@redhat.com>
Acked-by: default avatarChristian König <christian.koenig@amd.com>
parent 45db3370

Documentation/admin-guide/kernel-parameters.txt

+9 −0
Original line number Diff line number Diff line
@@ -3192,6 +3192,15 @@ 
				Adding the window is slightly risky (it may

				conflict with unreported devices), so this

				taints the kernel.

		disable_acs_redir=<pci_dev>[; ...]

				Specify one or more PCI devices (in the format

				specified above) separated by semicolons.

				Each device specified will have the PCI ACS

				redirect capabilities forced off which will

				allow P2P traffic between devices through

				bridges without forcing it upstream. Note:

				this removes isolation between devices and

				may put more devices in an IOMMU group.



	pcie_aspm=	[PCIE] Forcibly enable or disable PCIe Active State Power

			Management.

drivers/pci/pci.c

+71 −2
Original line number Diff line number Diff line
@@ -2982,6 +2982,63 @@ void pci_request_acs(void) 
	pci_acs_enable = 1;

}



static const char *disable_acs_redir_param;



/**

 * pci_disable_acs_redir - disable ACS redirect capabilities

 * @dev: the PCI device

 *

 * For only devices specified in the disable_acs_redir parameter.

 */

static void pci_disable_acs_redir(struct pci_dev *dev)

{

	int ret = 0;

	const char *p;

	int pos;

	u16 ctrl;



	if (!disable_acs_redir_param)

		return;



	p = disable_acs_redir_param;

	while (*p) {

		ret = pci_dev_str_match(dev, p, &p);

		if (ret < 0) {

			pr_info_once("PCI: Can't parse disable_acs_redir parameter: %s\n",

				     disable_acs_redir_param);



			break;

		} else if (ret == 1) {

			/* Found a match */

			break;

		}



		if (*p != ';' && *p != ',') {

			/* End of param or invalid format */

			break;

		}

		p++;

	}



	if (ret != 1)

		return;



	pos = pci_find_ext_capability(dev, PCI_EXT_CAP_ID_ACS);

	if (!pos) {

		pci_warn(dev, "cannot disable ACS redirect for this hardware as it does not have ACS capabilities\n");

		return;

	}



	pci_read_config_word(dev, pos + PCI_ACS_CTRL, &ctrl);



	/* P2P Request & Completion Redirect */

	ctrl &= ~(PCI_ACS_RR | PCI_ACS_CR | PCI_ACS_EC);



	pci_write_config_word(dev, pos + PCI_ACS_CTRL, ctrl);



	pci_info(dev, "disabled ACS redirect\n");

}



/**

 * pci_std_enable_acs - enable ACS on devices using standard ACS capabilites

 * @dev: the PCI device
@@ -3021,12 +3078,22 @@ static void pci_std_enable_acs(struct pci_dev *dev) 
void pci_enable_acs(struct pci_dev *dev)

{

	if (!pci_acs_enable)

		return;

		goto disable_acs_redir;



	if (!pci_dev_specific_enable_acs(dev))

		return;

		goto disable_acs_redir;



	pci_std_enable_acs(dev);



disable_acs_redir:

	/*

	 * Note: pci_disable_acs_redir() must be called even if ACS was not

	 * enabled by the kernel because it may have been enabled by

	 * platform firmware.  So if we are told to disable it, we should

	 * always disable it after setting the kernel's default

	 * preferences.

	 */

	pci_disable_acs_redir(dev);

}



static bool pci_acs_flags_enabled(struct pci_dev *pdev, u16 acs_flags)
@@ -5966,6 +6033,8 @@ static int __init pci_setup(char *str) 
				pcie_bus_config = PCIE_BUS_PEER2PEER;

			} else if (!strncmp(str, "pcie_scan_all", 13)) {

				pci_add_flags(PCI_SCAN_ALL_PCIE_DEVS);

			} else if (!strncmp(str, "disable_acs_redir=", 18)) {

				disable_acs_redir_param = str + 18;

			} else {

				printk(KERN_ERR "PCI: Unknown option `%s'\n",

						str);

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