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

From: Alexey Kardashevskiy <[email-masked]>
Date: Fri, 7 Aug 2015 17:14:41 +1000

On 08/07/2015 12:24 PM, 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.

If we are not going to use non-64bit IOV BAR, why would we assign anything 
to it at the first place? Or it is a common PCI code which does it?

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

-- 
Alexey