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Date:	Tue, 7 Oct 2014 18:02:09 +0300
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	Marcel Apfelbaum <marcel.a@...hat.com>
Cc:	linux-pci@...r.kernel.org, bhelgaas@...gle.com,
	linux-kernel@...r.kernel.org, marcel@...hat.com,
	alex.williamson@...hat.com
Subject: Re: [PATCH v3] PCI: add kernel parameter to override devid<->driver
 mapping.

On Tue, Oct 07, 2014 at 05:48:32PM +0300, Marcel Apfelbaum wrote:
> 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

Do we know all drivers have shorter names?

> +
> +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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