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

[Marcel Apfelbaum <marcel.a@redhat.com>]

On Wed, 2014-10-01 at 09:52 +0300, Michael S. Tsirkin wrote:
> On Tue, Sep 30, 2014 at 07:38:35PM +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 slot 0001:02:03.4 to pci-stub use:
> > 	driver[0001:02:03.4]=pci-stub
> > 
> > Signed-off-by: Marcel Apfelbaum <marcel.a@redhat.com>
> > ---
> > 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);
> 
> 
Hi,

> You allocate this entry but never free it?
Is being freed in pci_release_dev function.

> Shouldn't allocation failure be handled in some way?
I thought about it, but in my opinion there is no need for error
handling in this situation.
- On the worst case scenario it will load the regular driver, no harm done.
  (kstrndup will return NULL)
- It is used in pci_bus_add_device workflow that has no error flow
  that I am aware of, and even if it were an error flow, in my opinion
  this is not enough to stop system boot.
But thinking of this again, maybe a pr_err message?

Your review is most appreciated.
Thanks,
Marcel


> 
> > +		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