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: Thu, 6 Aug 2015 21:07:01 +1000

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"?
>

It's a confusing message: It's not related to space and M64 window.
When any VF BAR is IO or M32, we just give up attempting to allocate
resources for it. I still think my original message is enough or
similarly below one:

	dev_warn(&pdev->dev, "Disabled SRIOV because of non-M64 BAR"

>>
>>>>
>>>>
>>>>>		/* 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
>