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Date: Tue, 11 Apr 2017 15:51:34 -0600
From: Alex Williamson <alex.williamson@...hat.com>
To: bodong@...lanox.com
Cc: bhelgaas@...gle.com, linux-pci@...r.kernel.org,
linux-kernel@...r.kernel.org, saeedm@...lanox.com,
Eli Cohen <eli@...lanox.com>
Subject: Re: [v2] PCI: Add an option to control probing of VFs before
enabling SR-IOV
On Wed, 22 Mar 2017 17:53:58 +0200
bodong@...lanox.com wrote:
> From: Bodong Wang <bodong@...lanox.com>
>
> Sometimes it is not desirable to probe the virtual functions after
> SRIOV is enabled. This can save host side resource usage by VF
> instances which would be eventually probed to VMs.
>
> Add a new PCI sysfs interface "sriov_probe_vfs" to control that
> from the PF, all current callers still retain the same functionality.
> To modify it, echo 0/n/N (disable probe) or 1/y/Y (enable probe) to
>
> /sys/bus/pci/devices/<DOMAIN:BUS:DEVICE.FUNCTION>/sriov_probe_vfs
>
> Note that, the choice must be made before enabling VFs. The change
> will not take effect if VFs are already enabled. Simply, one can set
> sriov_numvfs to 0, choose whether to probe or not, and then resume
> sriov_numvfs.
>
> Signed-off-by: Bodong Wang <bodong@...lanox.com>
> Signed-off-by: Eli Cohen <eli@...lanox.com>
> Reviewed-by: Gavin Shan <gwshan@...ux.vnet.ibm.com>
> ---
> Documentation/PCI/pci-iov-howto.txt | 10 ++++++++++
> drivers/pci/iov.c | 1 +
> drivers/pci/pci-driver.c | 22 ++++++++++++++++++----
> drivers/pci/pci-sysfs.c | 28 ++++++++++++++++++++++++++++
> drivers/pci/pci.h | 1 +
> 5 files changed, 58 insertions(+), 4 deletions(-)
There should be an update to Documentation/ABI/testing/sysfs-bus-pci in
here too.
>
> diff --git a/Documentation/PCI/pci-iov-howto.txt b/Documentation/PCI/pci-iov-howto.txt
> index 2d91ae2..902a528 100644
> --- a/Documentation/PCI/pci-iov-howto.txt
> +++ b/Documentation/PCI/pci-iov-howto.txt
> @@ -68,6 +68,16 @@ To disable SR-IOV capability:
> echo 0 > \
> /sys/bus/pci/devices/<DOMAIN:BUS:DEVICE.FUNCTION>/sriov_numvfs
>
> +To enable probing VFs by a compatible driver on the host:
nit, probably a good idea to note that probing is enabled by default.
> +Before enabling SR-IOV capabilities, do:
> + echo 1 > \
> + /sys/bus/pci/devices/<DOMAIN:BUS:DEVICE.FUNCTION>/sriov_probe_vfs
> +
> +To disable probing VFs by a compatible driver on the host:
> +Before enabling SR-IOV capabilities, do:
> + echo 0 > \
> + /sys/bus/pci/devices/<DOMAIN:BUS:DEVICE.FUNCTION>/sriov_probe_vfs
> +
> 3.2 Usage example
>
> Following piece of code illustrates the usage of the SR-IOV API.
> diff --git a/drivers/pci/iov.c b/drivers/pci/iov.c
> index 2479ae8..70691de 100644
> --- a/drivers/pci/iov.c
> +++ b/drivers/pci/iov.c
> @@ -450,6 +450,7 @@ static int sriov_init(struct pci_dev *dev, int pos)
> iov->total_VFs = total;
> iov->pgsz = pgsz;
> iov->self = dev;
> + iov->probe_vfs = true;
> pci_read_config_dword(dev, pos + PCI_SRIOV_CAP, &iov->cap);
> pci_read_config_byte(dev, pos + PCI_SRIOV_FUNC_LINK, &iov->link);
> if (pci_pcie_type(dev) == PCI_EXP_TYPE_RC_END)
> diff --git a/drivers/pci/pci-driver.c b/drivers/pci/pci-driver.c
> index afa7271..2a1cf84 100644
> --- a/drivers/pci/pci-driver.c
> +++ b/drivers/pci/pci-driver.c
> @@ -394,6 +394,18 @@ void __weak pcibios_free_irq(struct pci_dev *dev)
> {
> }
>
> +#ifdef CONFIG_PCI_IOV
> +static inline bool pci_device_can_probe(struct pci_dev *pdev)
> +{
> + return (!pdev->is_virtfn || pdev->physfn->sriov->probe_vfs);
> +}
> +#else
> +static inline bool pci_device_can_probe(struct pci_dev *pdev)
> +{
> + return true;
> +}
> +#endif
> +
> static int pci_device_probe(struct device *dev)
> {
> int error;
> @@ -405,10 +417,12 @@ static int pci_device_probe(struct device *dev)
> return error;
>
> pci_dev_get(pci_dev);
> - error = __pci_device_probe(drv, pci_dev);
> - if (error) {
> - pcibios_free_irq(pci_dev);
> - pci_dev_put(pci_dev);
> + if (pci_device_can_probe(pci_dev)) {
> + error = __pci_device_probe(drv, pci_dev);
> + if (error) {
> + pcibios_free_irq(pci_dev);
> + pci_dev_put(pci_dev);
> + }
> }
>
> return error;
> diff --git a/drivers/pci/pci-sysfs.c b/drivers/pci/pci-sysfs.c
> index 25d010d..1d5b89d 100644
> --- a/drivers/pci/pci-sysfs.c
> +++ b/drivers/pci/pci-sysfs.c
> @@ -526,10 +526,37 @@ static ssize_t sriov_numvfs_store(struct device *dev,
> return count;
> }
>
> +static ssize_t sriov_probe_vfs_show(struct device *dev,
> + struct device_attribute *attr,
> + char *buf)
> +{
> + struct pci_dev *pdev = to_pci_dev(dev);
> +
> + return sprintf(buf, "%u\n", pdev->sriov->probe_vfs);
> +}
> +
> +static ssize_t sriov_probe_vfs_store(struct device *dev,
> + struct device_attribute *attr,
> + const char *buf, size_t count)
> +{
> + struct pci_dev *pdev = to_pci_dev(dev);
> + bool probe_vfs;
> +
> + if (kstrtobool(buf, &probe_vfs) < 0)
> + return -EINVAL;
> +
> + pdev->sriov->probe_vfs = probe_vfs;
> +
> + return count;
> +}
> +
> static struct device_attribute sriov_totalvfs_attr = __ATTR_RO(sriov_totalvfs);
> static struct device_attribute sriov_numvfs_attr =
> __ATTR(sriov_numvfs, (S_IRUGO|S_IWUSR|S_IWGRP),
> sriov_numvfs_show, sriov_numvfs_store);
> +static struct device_attribute sriov_probe_vfs_attr =
> + __ATTR(sriov_probe_vfs, (S_IRUGO|S_IWUSR|S_IWGRP),
> + sriov_probe_vfs_show, sriov_probe_vfs_store);
> #endif /* CONFIG_PCI_IOV */
>
> static ssize_t driver_override_store(struct device *dev,
> @@ -1549,6 +1576,7 @@ static umode_t pci_dev_hp_attrs_are_visible(struct kobject *kobj,
> static struct attribute *sriov_dev_attrs[] = {
> &sriov_totalvfs_attr.attr,
> &sriov_numvfs_attr.attr,
> + &sriov_probe_vfs_attr.attr,
> NULL,
> };
>
> diff --git a/drivers/pci/pci.h b/drivers/pci/pci.h
> index 8dd38e6..b7d8127d 100644
> --- a/drivers/pci/pci.h
> +++ b/drivers/pci/pci.h
> @@ -272,6 +272,7 @@ struct pci_sriov {
> struct pci_dev *self; /* this PF */
> struct mutex lock; /* lock for setting sriov_numvfs in sysfs */
> resource_size_t barsz[PCI_SRIOV_NUM_BARS]; /* VF BAR size */
> + bool probe_vfs; /* control probing of VFs */
> };
>
> #ifdef CONFIG_PCI_ATS
Aside from the missing ABI update and howto nit, this seems ok to me,
though I wonder if this isn't a more general problem that should maybe
be solved in the driver core for any device that may create/expose
child devices. The drivers_autoprobe interface we currently have is
pretty limited with its bus-subsystem level scope. Thanks,
Alex
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