[PATCH kernel] PCI: Disable IOV before pcibios_sriov_disable()

[Alexey Kardashevskiy]

From: Gavin Shan <gwshan at linux.vnet.ibm.com>

The PowerNV platform is the only user of pcibios_sriov_disable().
The IOV BAR could be shifted by pci_iov_update_resource(). The
warning message in the function is printed if the IOV capability
is in enabled (PCI_SRIOV_CTRL_VFE && PCI_SRIOV_CTRL_MSE) state.

This is the backtrace of what is happening:
   pci_disable_sriov
   sriov_disable
   pnv_pci_sriov_disable
   pnv_pci_vf_resource_shift
   pci_update_resource
   pci_iov_update_resource

This fixes the issue by disabling IOV capability before calling
pcibios_sriov_disable(). With it, the disabling path matches
the enabling path: pcibios_sriov_enable() is called before the
IOV capability is enabled.

Cc: shan.gavin at gmail.com
Cc: Benjamin Herrenschmidt <benh at kernel.crashing.org>
Cc: Paul Mackerras <paulus at samba.org>
Reported-by: Carol L Soto <clsoto at us.ibm.com>
Signed-off-by: Gavin Shan <gwshan at linux.vnet.ibm.com>
Tested-by: Carol L Soto <clsoto at us.ibm.com>
Signed-off-by: Alexey Kardashevskiy <aik at ozlabs.ru>
---

This is repost. Since Gavin left the team, I am trying to push it out.
The previos converstion is here: https://patchwork.ozlabs.org/patch/732653/

Two questions were raised then. I'll try to comment on this below.

>1) "res" is already in the resource tree, so we shouldn't be changing
>   its start address, because that may make the tree inconsistent,
>   e.g., the resource may no longer be completely contained in its
>   parent, it may conflict with a sibling, etc.

We should not, yes. But...

At the boot time IOV BAR gets as much MMIO space as it can possibly use.
(Embarassingly I cannot trace where this is coming from, 8GB is selected
via pci_assign_unassigned_root_bus_resources() path somehow).
For example, it is 256*32MB=8GB where 256 is maximum PEs number and 32MB
is a PF/VF BAR size. Whatever shifting we do afterwards, the boudaries of
that 8GB area do not change and we test it in pnv_pci_vf_resource_shift():

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/powerpc/platforms/powernv/pci-ioda.c#n987

> 2) If we update "res->start", shouldn't we update "res->end"
>   correspondingly?

We have to update the PF's IOV BAR address as we allocate PEs dynamically
and we do not know in advance where our VF numbers start in that
8GB window. So we change IOV BASR start. Changing the end may make it
look more like there is a free area to use but in reality it won't be
usable as well as the area we "release" by shifting the start address.

We could probably move that M64 MMIO window by the same delta in
opposite direction so the IOV BAR start address would remain the same
but its VF#0 would be mapped to let's say PF#5. I am just afraid there
is an alignment requirement for these M64 window start address; and this
would be even more tricky to manage.

We could also create reserved areas for the amount of space "release" by
moving the start address, not sure how though.

So how do we proceed with this particular patch now? Thanks.
---
 drivers/pci/iov.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/drivers/pci/iov.c b/drivers/pci/iov.c
index 120485d6f352..ac41c8be9200 100644
--- a/drivers/pci/iov.c
+++ b/drivers/pci/iov.c
@@ -331,7 +331,6 @@ static int sriov_enable(struct pci_dev *dev, int nr_virtfn)
 	while (i--)
 		pci_iov_remove_virtfn(dev, i, 0);
 
-	pcibios_sriov_disable(dev);
 err_pcibios:
 	iov->ctrl &= ~(PCI_SRIOV_CTRL_VFE | PCI_SRIOV_CTRL_MSE);
 	pci_cfg_access_lock(dev);
@@ -339,6 +338,8 @@ static int sriov_enable(struct pci_dev *dev, int nr_virtfn)
 	ssleep(1);
 	pci_cfg_access_unlock(dev);
 
+	pcibios_sriov_disable(dev);
+
 	if (iov->link != dev->devfn)
 		sysfs_remove_link(&dev->dev.kobj, "dep_link");
 
@@ -357,14 +358,14 @@ static void sriov_disable(struct pci_dev *dev)
 	for (i = 0; i < iov->num_VFs; i++)
 		pci_iov_remove_virtfn(dev, i, 0);
 
-	pcibios_sriov_disable(dev);
-
 	iov->ctrl &= ~(PCI_SRIOV_CTRL_VFE | PCI_SRIOV_CTRL_MSE);
 	pci_cfg_access_lock(dev);
 	pci_write_config_word(dev, iov->pos + PCI_SRIOV_CTRL, iov->ctrl);
 	ssleep(1);
 	pci_cfg_access_unlock(dev);
 
+	pcibios_sriov_disable(dev);
+
 	if (iov->link != dev->devfn)
 		sysfs_remove_link(&dev->dev.kobj, "dep_link");
 
-- 
2.11.0