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Date:	Thu, 23 Oct 2014 15:32:01 +0300
From:	Marcel Apfelbaum <marcel.a@...hat.com>
To:	Alex Williamson <alex.williamson@...hat.com>
Cc:	linux-pci@...r.kernel.org, bhelgaas@...gle.com,
	linux-kernel@...r.kernel.org, marcel@...hat.com, mst@...hat.com,
	Stuart Yoder <stuart.yoder@...escale.com>
Subject: Re: [PATCH v4] PCI: add kernel parameter to override devid<->driver
 mapping.

On Wed, 2014-10-22 at 12:32 -0600, Alex Williamson wrote:
> [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@...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>
> > ---
> > 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.
The real question here if those bus types/devices would benefit from this
feature, and I also must confess that I have no knowledge of the other buses.
Can anyone confirm that it does make sense for them?

> 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?
For PCI, sure the domain:bus:dev.func is unique, for platform I have no idea,
can anyone that knows "platform" confirm or deny?

> 
> 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 way I see it is simple, the override specified in kernel command line
last as long as the user does not specifically remove it using
echo "" > /sys/.../driver_override
and then unbind and bind the device again.

>   The only option here seems to be a reboot.
Please see above

> Do we need a /sys/bus/pci/driver_overrides/{add_name,remove_name} for
> this interface?  Thanks,
While it does not hurt, I see it as optional since a simple removal of
driver_override and rebind does the same

Thanks,
Marcel

> 
> 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);
> 
> 
> 



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