Re: [v2] PCI: Add an option to control probing of VFs before enabling SR-IOV

[Alex Williamson <alex.williamson@redhat.com>]

On Wed, 22 Mar 2017 17:53:58 +0200
bodong@mellanox.com wrote:

> From: Bodong Wang <bodong@mellanox.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@mellanox.com>
> Signed-off-by: Eli Cohen <eli@mellanox.com>
> Reviewed-by: Gavin Shan <gwshan@linux.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