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Date:	Thu, 23 Oct 2014 07:11:50 -0600
From:	Alex Williamson <alex.williamson@...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, mst@...hat.com,
	Stuart Yoder <stuart.yoder@...escale.com>
Subject: Re: [PATCH v4] PCI: add kernel parameter to override devid<->driver
 mapping.


On Thu, 2014-10-23 at 15:32 +0300, Marcel Apfelbaum wrote:
> 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?

Platform devices are adding vfio support, so I expect the next logical
question will be how to reserve devices for use by vfio at boot.

> > 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

That's only a temporary removal though, if the device is removed and
re-added, either via physical hotplug or sysfs, the override is
re-applied.  Thanks,

Alex

> > 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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