On Thu, 2017-09-14 at 13:18 +1000, Alexey Kardashevskiy wrote: > On 14/09/17 13:07, Benjamin Herrenschmidt wrote: > > On Thu, 2017-09-14 at 12:45 +1000, Alexey Kardashevskiy wrote: > > > On 31/08/17 13:34, Alexey Kardashevskiy wrote: > > > > From: Benjamin Herrenschmidt <b...@kernel.crashing.org> > > > > > > Oops, this was not right :) > > > > > > Anyway, Ben, please comment. Thanks. > > > > This is incorrect, we can do hotplug behind switches afaik. > > Do we have an actual system which allows this?
Tuleta no ? > Anyway, what we do now is > wrong and it needs what? Reserve that hole? I'd like to update the comment > for now, at least, and state what bad thing can happen and what we expect. The hole should be reserved unless another SR-IOV device can use it ... > > > > > > > > > > > > From: Alexey Kardashevskiy <a...@ozlabs.ru> > > > > > > > > This updates the comment about creating a hole in /proc/iomem which > > > > should not be normally happening but it does in the powernv platform > > > > due the way MMIO M64 BARs are organised in the IODA2-capable hardware. > > > > > > > > Signed-off-by: Alexey Kardashevskiy <a...@ozlabs.ru> > > > > --- > > > > > > > > It has been mentioned multiple times (last one - > > > > https://www.spinics.net/lists/linux-pci/msg64084.html ) that the comment > > > > is not informative enough for people not particularly familiar with > > > > the POWER8 IO hardware. > > > > > > > > This attempt aims to: > > > > 1. explain why we shift the resource > > > > 2. explain why nothing can use that hole as a resource while it is > > > > "free" > > > > (I am not sure that this is the case actually) > > > > > > > > Please comment, everyone, let's have this very well documented while > > > > I remember these bits :) Thanks. > > > > --- > > > > arch/powerpc/platforms/powernv/pci-ioda.c | 10 +++++++--- > > > > 1 file changed, 7 insertions(+), 3 deletions(-) > > > > > > > > diff --git a/arch/powerpc/platforms/powernv/pci-ioda.c > > > > b/arch/powerpc/platforms/powernv/pci-ioda.c > > > > index 48de308224d6..c4a36ae78c95 100644 > > > > --- a/arch/powerpc/platforms/powernv/pci-ioda.c > > > > +++ b/arch/powerpc/platforms/powernv/pci-ioda.c > > > > @@ -1002,9 +1002,13 @@ static int pnv_pci_vf_resource_shift(struct > > > > pci_dev *dev, int offset) > > > > } > > > > > > > > /* > > > > - * 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. > > > > + * Since M64 BAR shares segments among all possible 256 PEs, > > > > + * we have to shift the beginning of PF IOV BAR to make it > > > > start from > > > > + * the segment which belongs to the PE number assigned to the > > > > first VF. > > > > + * This creates a "hole" in the /proc/iomem which could be used > > > > for > > > > + * allocating other resources, however this is not expected to > > > > happen > > > > + * on IODA as the only possibility would be a PCI hotplug and > > > > IODA > > > > + * hardware only allows it on a slot with dedicated PHB. > > > > */ > > > > for (i = 0; i < PCI_SRIOV_NUM_BARS; i++) { > > > > res = &dev->resource[i + PCI_IOV_RESOURCES]; > > > > > > > > > > > >
