> Subject: RE: Why does BIOS assign memory to 16 byte BAR > > > Subject: RE: Why does BIOS assign memory to 16 byte BAR > > > > > Subject: Re: Why does BIOS assign memory to 16 byte BAR > > > > > > On Fri, Jul 22, 2016 at 10:15:46AM -0500, Bjorn Helgaas wrote: > > > > Hi Bharat, > > > > > > > > On Fri, Jul 22, 2016 at 09:24:22AM +0000, Bharat Kumar Gogada wrote: > > > > > Hi, > > > > > > > > > > I'm observing that on x86 BIOS successfully assigns memory if an End > > > > > point requests BAR of size 16byte. > > > > > > > > > > But as per Spec: > > > > > The minimum memory address range requested by a BAR is 128 > bytes. > > > > > > > > Can you provide the spec reference for this? I don't see it in PCI > > > > r3.0. > > > > > > > > PCI r3.0, sec 6.2.5.1, shows bits 4-31 of a memory BAR as writable, > > > > which would correspond to a minimum size of 16 bytes. > > > > > > The reference above is to the conventional PCI spec. I happened to trip > > over > > > a note in PCIe r3.0, sec 1.3.2.2, that for a PCI Express endpoint, "the > > minimum > > > memory address range requested by a BAR is 128 bytes." > > > > > > I don't think linux currently enforces this minimum. > > > > > > > Hi Bjorn Thanks for the reply. > > > > Here is what the issue we are seeing. > > > > We have total memory for BAR's on our SoC of 256 MB. > > When an End Point request individually 16 byte BAR's our root port assigns > > memory to BAR's successfully. > > > > But if I have an End point which has 4 BAR's each 32 bit and request as > > following: > > When 1st BAR requests 1GB BAR it fails due to lack of memory. (We are > > running this as part of SIG compliance test case) > > 2nd BAR requests 1MB and other 2 BAR's request 16byte, but these are not > > getting BAR's assigned. (Even though BAR space is available, since 1GB > failed, > > We have 256 MB still) > > > > We have only one End point connected to our root port. > > > > Here is the log: > > [ 2.319289] nwl-pcie fd0e0000.pcie: Link is UP > > [ 2.319332] PCI host bridge /amba/pcie@fd0e0000 ranges: > > [ 2.319349] No bus range found for /amba/pcie@fd0e0000, using [bus > 00- > > ff] > > [ 2.319374] IO 0xe0000000..0xe000ffff -> 0x00000000 > > [ 2.319415] MEM 0xe0100000..0xefffffff -> 0xe0100000 > > [ 2.319431] MEM 0x600000000..0x7ffffffff -> 0x600000000 > > [ 2.319539] nwl-pcie fd0e0000.pcie: PCI host bridge to bus 0000:00 > > [ 2.319557] pci_bus 0000:00: root bus resource [bus 00-ff] > > [ 2.319573] pci_bus 0000:00: root bus resource [io 0x0000-0xffff] > > [ 2.319589] pci_bus 0000:00: root bus resource [mem 0xe0100000- > 0xefffffff] > > [ 2.319606] pci_bus 0000:00: root bus resource [mem 0x600000000- > > 0x7ffffffff pref] > > [ 2.319845] pci 0000:00:00.0: cannot attach to SMMU, is it on the same > bus? > > [ 2.319861] iommu: Adding device 0000:00:00.0 to group 1 > > [ 2.320243] pci 0000:01:00.0: cannot attach to SMMU, is it on the same > bus? > > [ 2.320258] iommu: Adding device 0000:01:00.0 to group 1 > > [ 2.320313] pci 0000:00:00.0: BAR 8: no space for [mem size 0x60000000] > > [ 2.320331] pci 0000:00:00.0: BAR 8: failed to assign [mem size 0x60000000] > > [ 2.320349] pci 0000:00:00.0: BAR 6: assigned [mem 0xe0100000- > 0xe01007ff > > pref] > > [ 2.320374] pci 0000:01:00.0: BAR 0: no space for [mem size 0x40000000] > > [ 2.320390] pci 0000:01:00.0: BAR 0: failed to assign [mem size 0x40000000] > > [ 2.320407] pci 0000:01:00.0: BAR 4: no space for [mem size 0x00100000 > > 64bit] > > [ 2.320423] pci 0000:01:00.0: BAR 4: failed to assign [mem size 0x00100000 > > 64bit] > > [ 2.320446] pci 0000:01:00.0: BAR 2: no space for [mem size 0x00000010] > > [ 2.320461] pci 0000:01:00.0: BAR 2: failed to assign [mem size 0x00000010] > > [ 2.320477] pci 0000:01:00.0: BAR 3: no space for [mem size 0x00000010] > > [ 2.320493] pci 0000:01:00.0: BAR 3: failed to assign [mem size 0x00000010] > > [ 2.320509] pci 0000:00:00.0: PCI bridge to [bus 01-0c] > > > > Please let me know, what might might be the issue. > > > > Adding to the above will kernel allocate other memory BARs to an End Point > if > one BAR assignment fails ? > > What if the End Point has multiple function and say first function BAR > assignment failed, > will the kernel assign BAR's to second function on same bus and device ? > After debugging in function pci_bus_alloc_from_region we have two resources, One which is taken as parameter (let's say resA), other is from pci_bus_for_each_resource (let's say resB). The resA contains different start address from resB, I see that resB is obtained from device resource from bus->resource, but im unable to understand how resA (start address & size) gets its data. Can any one help me understand this so that I might know reason why 16byte BAR allocation failing after 1GB request. Regards, Bharat -- To unsubscribe from this list: send the line "unsubscribe linux-pci" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
