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

From: Wei Yang <[email-masked]>
Date: Thu, 6 Aug 2015 22:13:32 +0800

On Thu, Aug 06, 2015 at 05:47:42PM +1000, Alexey Kardashevskiy wrote:
>On 08/06/2015 04:57 PM, Gavin Shan wrote:
>>On Thu, Aug 06, 2015 at 04:10:21PM +1000, Alexey Kardashevskiy wrote:
>>>On 08/06/2015 02:35 PM, 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.
>
>
>The proper text would be something like this:
>
>===
>SRIOV only supports 64bit MMIO. So if we fail to assign 64bit BAR, we
>cannot enable the device.
>===
>
>
>>>>>
>>>>
>>>>s/PHB_IODA2/PHB3
>>>
>>>
>>>No, it is IODA2. OPEL does PHB3-specific bits, the host kernel just uses OPAL.
>>>
>>
>>Ok.
>>
>>>
>>>>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");
>>>
>>>
>>>Both messages are cryptic.
>>>
>>>If it is not M64 BAR, then what is it? It is always in one of M64 BARs (in
>>>the worst case - BAR#15?), the difference is if it is segmented or not, no?
>>>
>>
>>The VF BAR could be one of IO, M32, M64. If it's not M64, the VFs are supposed
>>to be disabled and the (IO and M32) resources won't be allocted, but for sure,
>>the IO and M32 resources can't be put into any one of the 16 PHB's M64 BARs.
>>would you recommend one better message then?
>
>
>
>dev_warn(&pdev->dev, "SRIOV is disabled as no space is left in 64bit
>MMIO window\n");
>
>Or it is not "MMIO window"?
>

The reason is not "no space left in 64bit MMIO window".

The reason is the IOV BAR is not 64bit prefetchable, then in linux kernel this
can't be allocated from M64 Space, then we can't use M64 BAR to cover it.

>
>
>>
>>>>
>>>>
>>>>>		/* 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.
>>>>
>>>>>
>>>>>		dev_dbg(&pdev->dev, " Fixing VF BAR%d: %pR to\n", i, res);
>>>>>		size = pci_iov_resource_size(pdev, i + PCI_IOV_RESOURCES);
>
>
>-- 
>Alexey

-- 
Richard Yang
Help you, Help me