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: Thu, 6 Aug 2015 17:47:42 +1000

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"?

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