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





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