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. > > 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]; > -- Alexey
