Subject: Re: [PATCH V2 1/6] powerpc/powernv: don't enable SRIOV when VF BAR contains non M64 BAR

From: Gavin Shan <[email-masked]>
Date: Fri, 7 Aug 2015 13:50:37 +1000

On Fri, Aug 07, 2015 at 10:24:05AM +0800, Wei Yang wrote:
>On Fri, Aug 07, 2015 at 11:20:10AM +1000, Gavin Shan wrote:
>>On Thu, Aug 06, 2015 at 10:10:10PM +0800, Wei Yang wrote:
>>>On Thu, Aug 06, 2015 at 02:35:57PM +1000, Gavin Shan wrote:
>>>>On Wed, Aug 05, 2015 at 09:24:58AM +0800, Wei Yang wrote:
>>>>>On PHB_IODA2, we enable SRIOV devices by mapping IOV BAR with M64 BARs. If
>>>>>a SRIOV device's BAR is not 64-bit prefetchable, this is not assigned from
>>>>>M64 windwo, which means M64 BAR can't work on it.
>>>>>
>>>>
>>>>s/PHB_IODA2/PHB3
>>>>s/windwo/window
>>>>
>>>>>This patch makes this explicit.
>>>>>
>>>>>Signed-off-by: Wei Yang <[email-masked]>
>>>>
>>>>The idea sounds right, but there is one question as below.
>>>>
>>>>>---
>>>>> arch/powerpc/platforms/powernv/pci-ioda.c |   25 +++++++++----------------
>>>>> 1 file changed, 9 insertions(+), 16 deletions(-)
>>>>>
>>>>>diff --git a/arch/powerpc/platforms/powernv/pci-ioda.c b/arch/powerpc/platforms/powernv/pci-ioda.c
>>>>>index 5738d31..9b41dba 100644
>>>>>--- a/arch/powerpc/platforms/powernv/pci-ioda.c
>>>>>+++ b/arch/powerpc/platforms/powernv/pci-ioda.c
>>>>>@@ -908,9 +908,6 @@ static int pnv_pci_vf_resource_shift(struct pci_dev *dev, int offset)
>>>>> 		if (!res->flags || !res->parent)
>>>>> 			continue;
>>>>>
>>>>>-		if (!pnv_pci_is_mem_pref_64(res->flags))
>>>>>-			continue;
>>>>>-
>>>>> 		/*
>>>>> 		 * The actual IOV BAR range is determined by the start address
>>>>> 		 * and the actual size for num_vfs VFs BAR.  This check is to
>>>>>@@ -939,9 +936,6 @@ static int pnv_pci_vf_resource_shift(struct pci_dev *dev, int offset)
>>>>> 		if (!res->flags || !res->parent)
>>>>> 			continue;
>>>>>
>>>>>-		if (!pnv_pci_is_mem_pref_64(res->flags))
>>>>>-			continue;
>>>>>-
>>>>> 		size = pci_iov_resource_size(dev, i + PCI_IOV_RESOURCES);
>>>>> 		res2 = *res;
>>>>> 		res->start += size * offset;
>>>>>@@ -1221,9 +1215,6 @@ static int pnv_pci_vf_assign_m64(struct pci_dev *pdev, u16 num_vfs)
>>>>> 		if (!res->flags || !res->parent)
>>>>> 			continue;
>>>>>
>>>>>-		if (!pnv_pci_is_mem_pref_64(res->flags))
>>>>>-			continue;
>>>>>-
>>>>> 		for (j = 0; j < vf_groups; j++) {
>>>>> 			do {
>>>>> 				win = find_next_zero_bit(&phb->ioda.m64_bar_alloc,
>>>>>@@ -1510,6 +1501,12 @@ int pnv_pci_sriov_enable(struct pci_dev *pdev, u16 num_vfs)
>>>>> 	pdn = pci_get_pdn(pdev);
>>>>>
>>>>> 	if (phb->type == PNV_PHB_IODA2) {
>>>>>+		if (!pdn->vfs_expanded) {
>>>>>+			dev_info(&pdev->dev, "don't support this SRIOV device"
>>>>>+				" with non M64 VF BAR\n");
>>>>>+			return -EBUSY;
>>>>>+		}
>>>>>+
>>>>
>>>>It would be -ENOSPC since -EBUSY indicates the devices (VFs) are temparily
>>>>unavailable. For this case, the VFs are permanently unavailable because of
>>>>running out of space to accomodate M64 and non-M64 VF BARs.
>>>>
>>>>The error message could be printed with dev_warn() and it would be precise
>>>>as below or something else you prefer:
>>>>
>>>>	dev_warn(&pdev->dev, "SRIOV not supported because of non-M64 VF BAR\n");
>>>>
>>>
>>>Thanks for the comment, will change accordingly.
>>>
>>>>
>>>>> 		/* Calculate available PE for required VFs */
>>>>> 		mutex_lock(&phb->ioda.pe_alloc_mutex);
>>>>> 		pdn->offset = bitmap_find_next_zero_area(
>>>>>@@ -2774,9 +2771,10 @@ static void pnv_pci_ioda_fixup_iov_resources(struct pci_dev *pdev)
>>>>> 		if (!res->flags || res->parent)
>>>>> 			continue;
>>>>> 		if (!pnv_pci_is_mem_pref_64(res->flags)) {
>>>>>-			dev_warn(&pdev->dev, " non M64 VF BAR%d: %pR\n",
>>>>>+			dev_warn(&pdev->dev, "Don't support SR-IOV with"
>>>>>+					" non M64 VF BAR%d: %pR. \n",
>>>>> 				 i, res);
>>>>>-			continue;
>>>>>+			return;
>>>>> 		}
>>>>>
>>>>> 		size = pci_iov_resource_size(pdev, i + PCI_IOV_RESOURCES);
>>>>>@@ -2795,11 +2793,6 @@ static void pnv_pci_ioda_fixup_iov_resources(struct pci_dev *pdev)
>>>>> 		res = &pdev->resource[i + PCI_IOV_RESOURCES];
>>>>> 		if (!res->flags || res->parent)
>>>>> 			continue;
>>>>>-		if (!pnv_pci_is_mem_pref_64(res->flags)) {
>>>>>-			dev_warn(&pdev->dev, "Skipping expanding VF BAR%d: %pR\n",
>>>>>-				 i, res);
>>>>>-			continue;
>>>>>-		}
>>>>
>>>>When any one IOV BAR on the PF is non-M64, none of the VFs can be enabled.
>>>>Will we still allocate/assign M64 or M32 resources for the IOV BARs? If so,
>>>>I think it can be avoided.
>>>>
>>>
>>>Don't get your point. You mean to avoid this function?
>>>
>>>Or clear the IOV BAR when we found one of it is non-M64?
>>>
>>
>>I mean to clear all IOV BARs in case any more of them are IO or M32. In this
>>case, the SRIOV capability won't be enabled. Otherwise, the resources for
>>all IOV BARs are assigned and allocated by PCI subsystem, but they won't
>>be used. Does it make sense to you?
>>
>
>If we want to save MMIO space, this is not necessary.
>
>The IOV BAR will be put into the optional list in assignment stage. So when
>there is not enough MMIO space, they will not be assigned.
>

Why it's not necessary? The problem isn't related to MMIO space - enough, or
not enough as I explained above. Lets have an example here: PF has two
IOV BARs. One of the them is M32 BAR and the other is M64 BAR. For this case,
the SRIOV won't be enabled on the PF. Will the code still assign M32 resources
and M64 resources for those VF BARs (or IOV BARs)? If so, those VF BARs are
never used. Aren't we wasting resources? And how much MMIO resources are wasted
in this case?

>For the long term, maybe P9/P10, we will finally adjust the solution to
>support SRIOV devices with M32 MMIO. So I suggest to leave as it is.
>

I don't see how this problem is specific to P8. However, if you don't want
to improve this case currently. I'm fine. somebody can improve it in future.

>>>>>
>>>>> 		dev_dbg(&pdev->dev, " Fixing VF BAR%d: %pR to\n", i, res);
>>>>> 		size = pci_iov_resource_size(pdev, i + PCI_IOV_RESOURCES);
>>>>>-- 
>>>>>1.7.9.5
>>>>>
>>>
>>>-- 
>>>Richard Yang
>>>Help you, Help me
>
>-- 
>Richard Yang
>Help you, Help me