Subject: Re: [PATCH V9 08/18] powrepc/pci: Refactor pci_dn

From: Bjorn Helgaas <[email-masked]>
Date: Wed, 19 Nov 2014 16:30:24 -0700

On Sun, Nov 02, 2014 at 11:41:24PM +0800, Wei Yang wrote:
> From: Gavin Shan <[email-masked]>
> 
> pci_dn is the extension of PCI device node and it's created from
> device node. Unfortunately, VFs that are enabled dynamically by
> PF's driver and they don't have corresponding device nodes, and
> pci_dn. The patch refactors pci_dn to support VFs:
> 
>    * pci_dn is organized as a hierarchy tree. VF's pci_dn is put
>      to the child list of pci_dn of PF's bridge. pci_dn of other
>      device put to the child list of pci_dn of its upstream bridge.
> 
>    * VF's pci_dn is expected to be created dynamically when applying
>      final fixup to PF. VF's pci_dn will be destroyed when releasing
>      PF's pci_dev instance. pci_dn of other device is still created
>      from device node as before.
> 
>    * For one particular PCI device (VF or not), its pci_dn can be
>      found from pdev->dev.archdata.firmware_data, PCI_DN(devnode),
>      or parent's list. The fast path (fetching pci_dn through PCI
>      device instance) is populated during early fixup time.
> 
> Signed-off-by: Gavin Shan <[email-masked]>
> ---
> ...

> +struct pci_dn *add_dev_pci_info(struct pci_dev *pdev)
> +{
> +#ifdef CONFIG_PCI_IOV
> +	struct pci_dn *parent, *pdn;
> +	int i;
> +
> +	/* Only support IOV for now */
> +	if (!pdev->is_physfn)
> +		return pci_get_pdn(pdev);
> +
> +	/* Check if VFs have been populated */
> +	pdn = pci_get_pdn(pdev);
> +	if (!pdn || (pdn->flags & PCI_DN_FLAG_IOV_VF))
> +		return NULL;
> +
> +	pdn->flags |= PCI_DN_FLAG_IOV_VF;
> +	parent = pci_bus_to_pdn(pdev->bus);
> +	if (!parent)
> +		return NULL;
> +
> +	for (i = 0; i < pci_sriov_get_totalvfs(pdev); i++) {
> +		pdn = add_one_dev_pci_info(parent, NULL,
> +					   pci_iov_virtfn_bus(pdev, i),
> +					   pci_iov_virtfn_devfn(pdev, i));

I'm not sure this makes sense, but I certainly don't know this code, so
maybe I'm missing something.

pci_iov_virtfn_bus() and pci_iov_virtfn_devfn() depend on
pdev->sriov->stride and pdev->sriov->offset.  These are read from VF Stride
and First VF Offset in the SR-IOV capability by sriov_init(), which is
called before add_dev_pci_info():

  pci_scan_child_bus
    pci_scan_slot
      pci_scan_single_device
	pci_device_add
	  pci_init_capabilities
	    pci_iov_init(PF)
	      sriov_init(PF, pos)
		pci_write_config_word(dev, pos + PCI_SRIOV_NUM_VF, 0)
		pci_read_config_word(dev, pos + PCI_SRIOV_VF_OFFSET, &offset)
		pci_read_config_word(dev, pos + PCI_SRIOV_VF_STRIDE, &stride)
		iov->offset = offset
		iov->stride = stride

  pci_bus_add_devices
    pci_bus_add_device
      pci_fixup_device(pci_fixup_final)
	add_dev_pci_info
	  pci_iov_virtfn_bus
	    return ... + sriov->offset + (sriov->stride * id) ...

But both First VF Offset and VF Stride change when ARI Capable Hierarchy or
NumVFs changes (SR-IOV spec sec 3.3.9, 3.3.10).  We set NumVFs to zero in
sriov_init() above.  We will change NumVFs to something different when a
driver calls pci_enable_sriov():

  pci_enable_sriov
    sriov_enable
      pci_write_config_word(dev, iov->pos + PCI_SRIOV_NUM_VF, nr_virtfn)

Now First VF Offset and VF Stride have changed from what they were when we
called pci_iov_virtfn_bus() above.

> +		if (!pdn) {
> +			pr_warn("%s: Cannot create firmware data "
> +				"for VF#%d of %s\n",
> +				__func__, i, pci_name(pdev));
> +			return NULL;
> +		}
> +	}
> +#endif
> +
> +	return pci_get_pdn(pdev);
> +}
> ...

> +static void pci_dev_pdn_create(struct pci_dev *pdev)
> +{
> +	add_dev_pci_info(pdev);
> +}
> +DECLARE_PCI_FIXUP_FINAL(PCI_ANY_ID, PCI_ANY_ID, pci_dev_pdn_create);

There are no other callers of add_dev_pci_info(), so it seems pointless to
declare it in arch/powerpc/include/asm/pci-bridge.h and add this wrapper
around it.

> +
> +static void pci_dev_pdn_setup(struct pci_dev *pdev)
> +{
> +	struct pci_dn *pdn;
> +
> +	if (pdev->dev.archdata.firmware_data)
> +		return;
> +
> +	/* Setup the fast path */
> +	pdn = pci_get_pdn(pdev);
> +	pdev->dev.archdata.firmware_data = pdn;
> +}
> +DECLARE_PCI_FIXUP_EARLY(PCI_ANY_ID, PCI_ANY_ID, pci_dev_pdn_setup);
> -- 
> 1.7.9.5
>