Re: [PATCH v4] PCI: add kernel parameter to override devid<->driver mapping.

[Alex Williamson <alex.williamson@redhat.com>]

[cc+ stuart]

On Mon, 2014-10-20 at 17:04 +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@redhat.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@redhat.com>
> ---
> v3 -> v4:
>  - Addressed Alex Williamson's comments:
>    - Modified the type of driver_override_entry's fields
>    - Used PCI_DEVFN when appropriated
>    - Removed redundant checks
>    - Replaced BUG_ON with pr_err messages
>    - Simpler command line parsing
>  - Addressed Michael S. Tsirkin comments
>    - removed DRIVER_OVERRIDE_NAME_LENGTH limitation
> 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                   | 111 ++++++++++++++++++++++++++++++++++++
>  drivers/pci/pci.c                   |   2 +
>  3 files changed, 117 insertions(+)

The driver_override feature that we're making use of here is also going
to be supported by platform devices and potentially more bustypes in the
future, so I'm concerned that making a pci specific kernel parameter is
too shortsighted.  Instead we could hook on to BUS_NOTIFY_ADD_DEVICE for
bustypes that support driver_override so we can have a common interface.
Perhaps:

driver_override=pci,0000:02:00.0=pci-stub;platform,fakename=vfio-platform

Finding delimiters that don't conflict may be challenging.  Also, can we
assume that bus-name:dev-name is unique for every bustype?  It is for
pci, platform?

It also seems like there's a question of how long should this override
last and how does the user disable it?  I think with pci-stub.ids=
$VENDOR:$DEVICE a user can echo the IDs to the pci-stub/remove_id sysfs
entry to cancel the effect.  The only option here seems to be a reboot.
Do we need a /sys/bus/pci/driver_overrides/{add_name,remove_name} for
this interface?  Thanks,

Alex

> 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..b49f5cc 100644
> --- a/drivers/pci/bus.c
> +++ b/drivers/pci/bus.c
> @@ -15,6 +15,8 @@
>  #include <linux/proc_fs.h>
>  #include <linux/slab.h>
>  
> +#include <asm/setup.h>
> +
>  #include "pci.h"
>  
>  void pci_add_resource_offset(struct list_head *resources, struct resource *res,
> @@ -230,6 +232,114 @@ EXPORT_SYMBOL(pci_bus_alloc_resource);
>  
>  void __weak pcibios_resource_survey_bus(struct pci_bus *bus) { }
>  
> +struct driver_override_entry {
> +	u16 domain;
> +	u8 bus;
> +	u8 devfn;
> +	char *driver_name;
> +	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  *buf;
> +	struct driver_override_entry *entry;
> +	int ret;
> +
> +	buf = kmalloc(COMMAND_LINE_SIZE, GFP_KERNEL);
> +	if (!buf)
> +		goto err_buf;
> +
> +	while (val) {
> +		char *k = strchr(val, ',');
> +
> +		if (k)
> +			*k++ = 0;
> +
> +		if (strncmp(val, "driver", 6)) {
> +			val = k;
> +			continue;
> +		}
> +
> +		memset(buf, 0, COMMAND_LINE_SIZE);
> +		ret = sscanf(val + 6, "[%4x:%2x:%2x.%2x]=%s",
> +			     &domain, &bus, &dev, &fn, buf);
> +		if (ret != 5) {
> +			pr_warn("PCI: Invalid command line: %s\n", val);
> +			val = k;
> +			continue;
> +		}
> +
> +		entry = kzalloc(sizeof(*entry), GFP_KERNEL);
> +		if (!entry)
> +			goto err_entry;
> +
> +		INIT_LIST_HEAD(&entry->list);
> +		entry->domain = domain;
> +		entry->bus = bus;
> +		entry->devfn = PCI_DEVFN(dev, fn);
> +		entry->driver_name = kstrdup(buf, GFP_KERNEL);
> +		if (!entry->driver_name)
> +			goto err_driver_name;
> +
> +		list_add_tail(&entry->list, &driver_override_entries);
> +		val = k;
> +	}
> +
> +	kfree(buf);
> +	return 0;
> +
> +err_driver_name:
> +	kfree(entry);
> +
> +err_entry:
> +	kfree(buf);
> +
> +err_buf:
> +	pr_err("PCI: Out of memory while parsing command line: %s\n", val);
> +	return -ENOMEM;
> +}
> +
> +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);
> +
> +		if (!cmdline)
> +			goto err_out_of_mem;
> +
> +		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);
> +		if (!dev->driver_override)
> +			goto err_out_of_mem;
> +
> +		break;
> +	}
> +
> +	return;
> +
> +err_out_of_mem:
> +	pr_err("PCI: Out of memory while setting up driver override\n");
> +}
> +
>  /**
>   * pci_bus_add_device - start driver for a single device
>   * @dev: device to add
> @@ -245,6 +355,7 @@ 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 625a4ac..37809d4 100644
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -4508,6 +4508,8 @@ 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);