[PATCH] PCI: add kernel parameter to override devid<->driver mapping.

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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@xxxxxxxxxx>
	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 slot 0001:02:03.4 to pci-stub use:
	driver[0001:02:03.4]=pci-stub

Signed-off-by: Marcel Apfelbaum <marcel.a@xxxxxxxxxx>
---
Notes:
 - For the moment only 32 slots can be assigned specific driver.
 - 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                   |  1 +
 drivers/pci/pci.c                   | 61 +++++++++++++++++++++++++++++++++++++
 drivers/pci/pci.h                   |  1 +
 4 files changed, 67 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..7a7ed85 100644
--- a/drivers/pci/bus.c
+++ b/drivers/pci/bus.c
@@ -245,6 +245,7 @@ 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..0a3e07c 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -4426,6 +4426,65 @@ void __weak pci_fixup_cardbus(struct pci_bus *bus)
 }
 EXPORT_SYMBOL(pci_fixup_cardbus);
 
+#define DRIVER_OVERRIDE_NAME_LENGTH 64
+#define DRIVER_OVERRIDE_MAP_SIZE 32
+
+struct driver_override_entry {
+	unsigned int domain;
+	unsigned char bus;
+	unsigned int devfn;
+	char driver_name[DRIVER_OVERRIDE_NAME_LENGTH];
+};
+
+static struct driver_override_entry __initdata
+	driver_override_map[DRIVER_OVERRIDE_MAP_SIZE];
+static int driver_override_num_entries __initdata;
+
+void pci_device_setup_driver_override(struct pci_dev *dev)
+{
+	int i;
+
+	for (i = 0; i < driver_override_num_entries; i++) {
+		if (pci_domain_nr(dev->bus) != driver_override_map[i].domain ||
+		    dev->bus->number != driver_override_map[i].bus ||
+		    dev->devfn != driver_override_map[i].devfn)
+			continue;
+
+		dev->driver_override = kstrndup(driver_override_map[i].driver_name,
+						DRIVER_OVERRIDE_NAME_LENGTH,
+						GFP_KERNEL);
+		break;
+	}
+}
+
+static void __init pci_parse_driver_override(char *str)
+{
+	unsigned int domain, bus, dev, fn;
+	char driver_name[DRIVER_OVERRIDE_NAME_LENGTH];
+	int ret, next_entry;
+	char format[] = "[%4x:%2x:%2x.%2x]=%%%ds";
+
+	sprintf(format + 18, "%%%ds", DRIVER_OVERRIDE_NAME_LENGTH);
+	ret = sscanf(str, format, &domain, &bus, &dev, &fn, driver_name);
+
+	if (ret != 5) {
+		pr_err("PCI: Invalid command line: driver%s\n", str);
+		return;
+	}
+
+	if (driver_override_num_entries == DRIVER_OVERRIDE_MAP_SIZE) {
+		pr_err("PCI: Driver map overflow - ignoring driver%s\n", str);
+		return;
+	}
+
+	next_entry = driver_override_num_entries++;
+	driver_override_map[next_entry].domain = domain;
+	driver_override_map[next_entry].bus = bus && 0xff;
+	driver_override_map[next_entry].devfn = ((dev & 0x1f) << 3) | (fn & 0x7);
+	memcpy(driver_override_map[next_entry].driver_name,
+	       driver_name, sizeof(driver_name));
+}
+
 static int __init pci_setup(char *str)
 {
 	while (str) {
@@ -4468,6 +4527,8 @@ 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)) {
+				pci_parse_driver_override(str + 6);
 			} else {
 				printk(KERN_ERR "PCI: Unknown option `%s'\n",
 						str);
diff --git a/drivers/pci/pci.h b/drivers/pci/pci.h
index 0601890..023d78b 100644
--- a/drivers/pci/pci.h
+++ b/drivers/pci/pci.h
@@ -197,6 +197,7 @@ enum pci_bar_type {
 bool pci_bus_read_dev_vendor_id(struct pci_bus *bus, int devfn, u32 *pl,
 				int crs_timeout);
 int pci_setup_device(struct pci_dev *dev);
+void pci_device_setup_driver_override(struct pci_dev *dev);
 int __pci_read_base(struct pci_dev *dev, enum pci_bar_type type,
 		    struct resource *res, unsigned int reg);
 int pci_resource_bar(struct pci_dev *dev, int resno, enum pci_bar_type *type);
-- 
1.8.3.1

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