On Tue, Mar 21, 2017 at 09:50:06AM +1100, Gavin Shan wrote: >On Mon, Mar 20, 2017 at 10:46:44AM -0500, Bjorn Helgaas wrote: >>On Sat, Mar 18, 2017 at 11:19:07AM +1100, Gavin Shan wrote: >>> On Thu, Mar 09, 2017 at 11:34:32AM +1100, Gavin Shan wrote: >>> >On Tue, Mar 07, 2017 at 02:15:29PM -0600, Bjorn Helgaas wrote: >>> >>On Mon, Feb 27, 2017 at 11:18:32AM +1100, Gavin Shan wrote: >>> >>> The PowerNV platform is the only user of pcibios_sriov_disable(). >>> >>> The IOV BAR could be shifted by pci_iov_update_resource(). The >>> >>> warning message in the function is printed if the IOV capability >>> >>> is in enabled (PCI_SRIOV_CTRL_VFE && PCI_SRIOV_CTRL_MSE) state. >>> >>> >>> >>> pci_disable_sriov >>> >>> sriov_disable >>> >>> pnv_pci_sriov_disable >>> >>> pnv_pci_vf_resource_shift >>> >>> pci_update_resource >>> >>> pci_iov_update_resource >>> >>> >>> >>> This fixes the issue by disabling IOV capability before calling >>> >>> pcibios_sriov_disable(). With it, the disabling path matches with >>> >>> the enabling path: pcibios_sriov_enable() is called before the >>> >>> IOV capability is enabled. >>> >> >>> >>I'm vaguely uncomfortable about this path: >>> >> >>> >> pci_disable_sriov >>> >> sriov_disable >>> >> pcibios_sriov_disable # powerpc version >>> >> pnv_pci_sriov_disable >>> >> pnv_pci_vf_resource_shift >>> >> res = &dev->resource[i + PCI_IOV_RESOURCES] >>> >> res->start += size * offset >>> >> pci_update_resource >>> >> pci_iov_update_resource >>> >> pnv_pci_vf_release_m64 >>> >> >>> >>1) "res" is already in the resource tree, so we shouldn't be changing >>> >> its start address, because that may make the tree inconsistent, >>> >> e.g., the resource may no longer be completely contained in its >>> >> parent, it may conflict with a sibling, etc. >>> >> >>> >>2) If we update "res->start", shouldn't we update "res->end" >>> >> correspondingly? >>> >> >>> >>It seems like it'd be better if we didn't update the device resources >>> >>in the enable/disable paths. If we could do the resource adjustments >>> >>earlier, somewhere before we give the device to a driver, it seems >>> >>like it would avoid these issues. >>> >> >>> >>We might have talked about these questions in the past, so I apologize >>> >>if you've already explained this. If that's the case, maybe we just >>> >>need some comments in the code to help the next confused reader. >>> >> >>> > >>> >Bjorn, thanks for review. I agree it's not perfect. We discussed this long >>> >time ago as I can remember. Let me try to make it a bit more clear: In our >>> >PHB hardware, there are 16 MMIO BARs. Each of them can be shared by 256 PEs >>> >(A) and owned exclusively by one PE (B). When VF BAR size is small enough, >>> >we take (A). Otherwise, we have to take (B). Only when taking (A), we need >>> >expand/move/shrink the IOV BAR. So lets stick to (A) for discussion here. >>> > >>> >Under (A), PF's IOV BAR size is extended to ((256 * (VF BAR size)) when the >>> >PF is probed. Then the @res, which corresponds to the IOV BAR, is assigned >>> >and put into the resource tree during resource sizing and assignment stage. >>> >The IOV capability is going to be enabled by PF's driver or sysfs entry, it >>> >calls into pnv_pci_sriov_enable() where number of contigous PEs (equal to >>> >number of VFs to be enabled) are allocated. We shift the IOV BAR base according >>> >to the starting PE number of the allocated block. Afterewards, the IOV BAR >>> >is restored when the IOV capability is disabled. So it's all about the PE. >>> >The IOV BAR's end address isn't touched, we needn't update @res->end when >>> >restoring the IOV BAR. >>> > >>> >In order to avoid moving IOV BAR base address, I need know the the PEs >>> >for the VFs before resourcd sizing and assignment stage. It means I need >>> >to reserve PEs in advance, which isn't nice because we never enable the >>> >VFs. In that case, the PEs are wasted. >>> > >>> >Yeah, it's nice to have add some comments in pnv_pci_vf_resource_shift() >>> >where pci_update_resource() is called. I will post another patch to >>> >linux-ppcdev and you'll be copied. If you agree, I think you can merge >>> >this patch as none of the concerns are too much related. >>> > >>> >>> Sorry, Bjorn, ping! Please let me know if there are more concerns you have. >> >>I think we had a misunderstanding -- you mentioned adding some >>comments and wrote "I will post another patch", and I *thought* you >>meant you were going to post another version of *this* patch with some >>updated comments. So I've been waiting for that updated patch. But I >>think you've been waiting for me to merge *this* patch as-is. >> >>To avoid having this discussion a third time in the future, I think >>you should add some comments at the point where you update the >>resource. Updating a resource after it's in the resource tree is >>clearly dangerous, so we need some explanation of why it's sort of OK >>in this particular case. >> >>If you can write a comment and dig up a URL to our previous >>discussion, I'd like to incorporate that into *this* patch before I >>merge it. The sooner we can document this, the less work it will be >>in the future. >> > >Ok. Sorry for the confusion and that I should looked into the code for more. >We already had one comment like below in arch/powerpc/platforms/powernv/pci-ioda.c:: >pnv_pci_vf_resource_shift(). I think it's exactly what you like to have, please >help to confirm. I believe it was added based on your comments long time ago when >you review the SRIOV (for PowerNV) patches. > > /* > * After doing so, there would be a "hole" in the /proc/iomem when > * offset is a positive value. It looks like the device return some > * mmio back to the system, which actually no one could use it. > */ > >http://www.spinics.net/lists/linux-pci/msg39424.html > Bjorn, please let me know if you have concerns. Thanks, Gavin
