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Date:	Tue,  7 Oct 2014 17:48:32 +0300
From:	Marcel Apfelbaum <marcel.a@...hat.com>
To:	linux-pci@...r.kernel.org, bhelgaas@...gle.com
Cc:	linux-kernel@...r.kernel.org, marcel@...hat.com, mst@...hat.com,
	alex.williamson@...hat.com
Subject: [PATCH v3] PCI: add kernel parameter to override devid<->driver mapping.

Scanning a lot of devices during boot requires a lot of time.
On other scenarios there is a need to bind a driver to a specific slot.

Binding devices to pci-stub driver does not work,
as it will not differentiate between devices of the
same type. Using some start scripts is error prone.

The solution leverages driver_override functionality introduced by

	commit: 782a985d7af26db39e86070d28f987cad21313c0
	Author: Alex Williamson <alex.williamson@...hat.com>
	Date:   Tue May 20 08:53:21 2014 -0600

    	PCI: Introduce new device binding path using pci_dev.driver_override

In order to bind PCI slots to specific drivers use:
	pci=driver[xxxx:xx:xx.x]=foo,driver[xxxx:xx:xx.x]=bar,...

Signed-off-by: Marcel Apfelbaum <marcel.a@...hat.com>
---
v2 -> v3:
 - Corrected subject line
v1 -> v2:
 - Addressed Michael S. Tsirkin comments
   - Removed 32 slots limitation
   - Better handling of memory allocation failures
     (preferred BUG_ON over error messages)
 - Addressed Alex Williamson's comments:
   - Modified commit message to show parameter usage more clear.
 - I preferred to re-use parse_args instead of manually using
   strstr in order to better comply with command line parsing
   rules.
 - I didn't use any locking when parsing the command line args
   (see parse_done usage) assuming that first call will be
   early in system boot and no race can occur. Please correct
   me if I am wrong.

Notes:
 - I have further ideas on top of this patch based on your reviews.
   I thought of:
   - Use wildcards to specify entire buses/devices, something like:
     	driver[0001:02:*.*]=pci-stub
   - Use comma to separate several devices:
     	driver[0001:02:03.4,0001:02:04.0,...]=pci-stub
   - Make domain optional:
   	driver[00:03.0]=pci-stub

Comments will be appreciated,
Thanks,
Marcel
 Documentation/kernel-parameters.txt |  4 ++
 drivers/pci/bus.c                   | 86 +++++++++++++++++++++++++++++++++++++
 drivers/pci/pci.c                   |  2 +
 3 files changed, 92 insertions(+)

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 5ae8608..c1cbb4c 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -2631,6 +2631,10 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
 		pcie_scan_all	Scan all possible PCIe devices.  Otherwise we
 				only look for one device below a PCIe downstream
 				port.
+		driver		Provide an override to the devid<->driver mapping
+				for a specific slot.
+				Bind PCI slot 0001:02:03.4 to pci-stub by:
+					driver[0001:02:03.4]=pci-stub
 
 	pcie_aspm=	[PCIE] Forcibly enable or disable PCIe Active State Power
 			Management.
diff --git a/drivers/pci/bus.c b/drivers/pci/bus.c
index 73aef51..d2c0721 100644
--- a/drivers/pci/bus.c
+++ b/drivers/pci/bus.c
@@ -230,6 +230,91 @@ EXPORT_SYMBOL(pci_bus_alloc_resource);
 
 void __weak pcibios_resource_survey_bus(struct pci_bus *bus) { }
 
+#define DRIVER_OVERRIDE_NAME_LENGTH 64
+
+struct driver_override_entry {
+	unsigned int domain;
+	unsigned char bus;
+	unsigned int devfn;
+	char driver_name[DRIVER_OVERRIDE_NAME_LENGTH];
+	struct list_head list;
+};
+
+static LIST_HEAD(driver_override_entries);
+
+static int pci_device_parse_driver_override(char *param, char *val,
+					    const char *unused)
+{
+	unsigned int domain, bus, dev, fn;
+	char driver_name[DRIVER_OVERRIDE_NAME_LENGTH];
+	char format[] = "[%4x:%2x:%2x.%2x]=%%%ds";
+	struct driver_override_entry *entry;
+	int ret;
+
+	while (val) {
+		char *k = strchr(val, ',');
+
+		if (k)
+			*k++ = 0;
+
+		if (strncmp(val, "driver", 6)) {
+			val = k;
+			continue;
+		}
+
+		sprintf(format + 18, "%%%ds", DRIVER_OVERRIDE_NAME_LENGTH);
+		ret = sscanf(val + 6, format, &domain, &bus, &dev, &fn,
+			     driver_name);
+		if (ret != 5) {
+			pr_err("PCI: Invalid command line: %s\n", val);
+			val = k;
+			continue;
+		}
+
+		entry = kzalloc(sizeof(*entry), GFP_KERNEL);
+		BUG_ON(!entry);
+
+		INIT_LIST_HEAD(&entry->list);
+		entry->domain = domain;
+		entry->bus = bus && 0xff;
+		entry->devfn = ((dev & 0x1f) << 3) | (fn & 0x7);
+		memcpy(entry->driver_name, driver_name, sizeof(driver_name));
+
+		list_add_tail(&entry->list, &driver_override_entries);
+		val = k;
+	}
+
+	return 0;
+}
+
+static void pci_device_setup_driver_override(struct pci_dev *dev)
+{
+	static int parse_done;
+	struct driver_override_entry *entry;
+
+	if (!parse_done) {
+		char *cmdline = kstrdup(saved_command_line, GFP_KERNEL);
+
+		BUG_ON(!cmdline);
+
+		parse_args("pci", cmdline, NULL,
+			   0, 0, 0, &pci_device_parse_driver_override);
+		kfree(cmdline);
+		parse_done = 1;
+	}
+
+	list_for_each_entry(entry, &driver_override_entries, list) {
+		if (pci_domain_nr(dev->bus) != entry->domain ||
+		    dev->bus->number != entry->bus ||
+		    dev->devfn != entry->devfn)
+			continue;
+
+		dev->driver_override = kstrdup(entry->driver_name, GFP_KERNEL);
+		BUG_ON(!dev->driver_override);
+		break;
+	}
+}
+
 /**
  * pci_bus_add_device - start driver for a single device
  * @dev: device to add
@@ -245,6 +330,7 @@ void pci_bus_add_device(struct pci_dev *dev)
 	 * are not assigned yet for some devices.
 	 */
 	pci_fixup_device(pci_fixup_final, dev);
+	pci_device_setup_driver_override(dev);
 	pci_create_sysfs_dev_files(dev);
 	pci_proc_attach_device(dev);
 
diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index b7678be..6bd7844 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -4468,6 +4468,8 @@ 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, "driver", 6)) {
+				/* lazy evaluation by the pci subsystem */
 			} else {
 				printk(KERN_ERR "PCI: Unknown option `%s'\n",
 						str);
-- 
1.8.3.1

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