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Message-ID: <1414002755.4202.253.camel@ul30vt.home>
Date: Wed, 22 Oct 2014 12:32:35 -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.
[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.
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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