Subject: Re: [PATCH v12 17/21] powerpc/powernv: Shift VF resource with an offset

From: Wei Yang <[email-masked]>
Date: Wed, 11 Mar 2015 14:42:15 +0800

On Tue, Mar 10, 2015 at 09:55:19PM -0500, Bjorn Helgaas wrote:
>On Wed, Mar 04, 2015 at 11:01:24AM +0800, Wei Yang wrote:
>> On Tue, Feb 24, 2015 at 03:00:37AM -0600, Bjorn Helgaas wrote:
>> >On Tue, Feb 24, 2015 at 02:34:57AM -0600, Bjorn Helgaas wrote:
>> >> From: Wei Yang <[email-masked]>
>> >> 
>> >> On PowerNV platform, resource position in M64 implies the PE# the resource
>> >> belongs to.  In some cases, adjustment of a resource is necessary to locate
>> >> it to a correct position in M64.
>> >> 
>> >> Add pnv_pci_vf_resource_shift() to shift the 'real' PF IOV BAR address
>> >> according to an offset.
>> >> 
>> >> [bhelgaas: rework loops, rework overlap check, index resource[]
>> >> conventionally, remove pci_regs.h include, squashed with next patch]
>> >> Signed-off-by: Wei Yang <[email-masked]>
>> >> Signed-off-by: Bjorn Helgaas <[email-masked]>
>> >
>> >...
>> >
>> >> +#ifdef CONFIG_PCI_IOV
>> >> +static int pnv_pci_vf_resource_shift(struct pci_dev *dev, int offset)
>> >> +{
>> >> +	struct pci_dn *pdn = pci_get_pdn(dev);
>> >> +	int i;
>> >> +	struct resource *res, res2;
>> >> +	resource_size_t size;
>> >> +	u16 vf_num;
>> >> +
>> >> +	if (!dev->is_physfn)
>> >> +		return -EINVAL;
>> >> +
>> >> +	/*
>> >> +	 * "offset" is in VFs.  The M64 windows are sized so that when they
>> >> +	 * are segmented, each segment is the same size as the IOV BAR.
>> >> +	 * Each segment is in a separate PE, and the high order bits of the
>> >> +	 * address are the PE number.  Therefore, each VF's BAR is in a
>> >> +	 * separate PE, and changing the IOV BAR start address changes the
>> >> +	 * range of PEs the VFs are in.
>> >> +	 */
>> >> +	vf_num = pdn->vf_pes;
>> >> +	for (i = 0; i < PCI_SRIOV_NUM_BARS; i++) {
>> >> +		res = &dev->resource[i + PCI_IOV_RESOURCES];
>> >> +		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 vf_num VFs BAR.  This check is to
>> >> +		 * make sure that after shifting, the range will not overlap
>> >> +		 * with another device.
>> >> +		 */
>> >> +		size = pci_iov_resource_size(dev, i + PCI_IOV_RESOURCES);
>> >> +		res2.flags = res->flags;
>> >> +		res2.start = res->start + (size * offset);
>> >> +		res2.end = res2.start + (size * vf_num) - 1;
>> >> +
>> >> +		if (res2.end > res->end) {
>> >> +			dev_err(&dev->dev, "VF BAR%d: %pR would extend past %pR (trying to enable %d VFs shifted by %d)\n",
>> >> +				i, &res2, res, vf_num, offset);
>> >> +			return -EBUSY;
>> >> +		}
>> >> +	}
>> >> +
>> >> +	for (i = 0; i < PCI_SRIOV_NUM_BARS; i++) {
>> >> +		res = &dev->resource[i + PCI_IOV_RESOURCES];
>> >> +		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;
>> >
>> >I'm still not happy about this fiddling with res->start.
>> >
>> >Increasing res->start means that in principle, the "size * offset" bytes
>> >that we just removed from res are now available for allocation to somebody
>> >else.  I don't think we *will* give that space to anything else because of
>> >the alignment restrictions you're enforcing, but "res" now doesn't
>> >correctly describe the real resource map.
>> >
>> >Would you be able to just update the BAR here while leaving the struct
>> >resource alone?  In that case, it would look a little funny that lspci
>> >would show a BAR value in the middle of the region in /proc/iomem, but
>> >the /proc/iomem region would be more correct.
>> 
>> Bjorn,
>> 
>> I did some tests, while the result is not good.
>> 
>> What I did is still write the shifted resource address to the device by
>> pci_update_resource(), but I revert the res->start to the original one. If
>> this step is not correct, please let me know.
>> 
>> This can't work since after we revert the res->start, those VFs will be given
>> resources from res->start instead of (res->start + offset * size). This is not
>> what we expect.
>
>Hmm, yes, I suppose we'd have to have a hook in pci_bus_alloc_from_region()
>or something.  That's getting a little messy.  I still don't like messing
>with the resource after it's in the resource tree, but I don't have a
>better idea right now.  So let's just go with what you have.
>

Thanks  :-)

I would state this in the change log and add a comment in the code to note
this down. Hope this would be a little helpful.

>> >> +
>> >> +		dev_info(&dev->dev, "VF BAR%d: %pR shifted to %pR (enabling %d VFs shifted by %d)\n",
>> >> +			 i, &res2, res, vf_num, offset);
>> >> +		pci_update_resource(dev, i + PCI_IOV_RESOURCES);
>> >> +	}
>> >> +	pdn->max_vfs -= offset;
>> >> +	return 0;
>> >> +}
>> >> +#endif /* CONFIG_PCI_IOV */
>> 
>> -- 
>> Richard Yang
>> Help you, Help me
>> 
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-- 
Richard Yang
Help you, Help me