On 01-Dec-17 12:12 AM, Bjorn Helgaas wrote: > On Thu, Nov 30, 2017 at 10:24:37AM +0000, Lorenzo Pieralisi wrote: >> On Wed, Nov 29, 2017 at 11:01:33AM -0600, Bjorn Helgaas wrote: >>> [+cc Lorenzo] >>> >>> On Sun, Nov 26, 2017 at 01:02:09AM +0530, Manikanta Maddireddy wrote: >>>> pci_flags variable is used in inline functions in 'pci.h', Tegra PCIe >>>> driver use one of these functions pci_add_flags() and includes 'pci.h'. >>>> Export pci_flags to allow Tegra PCIe host controller driver to be >>>> compiled as loadable kernel module. >>> >>> Here's the usage in tegra_pcie_probe(): >>> >>> pci_add_flags(PCI_REASSIGN_ALL_RSRC | PCI_REASSIGN_ALL_BUS); >>> >>> We've probably had this discussion before, but I don't know why Tegra >>> needs PCI_REASSIGN_ALL_RSRC and PCI_REASSIGN_ALL_BUS. >>> >>> I would prefer to drop this usage of pci_add_flags() if possible. It >>> seems to be just an arm/powerpc thing and I'm not convinced it's >>> really necessary. >> >> It is hard to say if it is really necessary (because it depends >> on firmware configuration - ie pci_scan_bridge()), that's the >> problem. >> >> I suspect it can trigger regressions if we do not set it (since >> it affects what pcibios_assign_all_busses() returns on eg arm/arm64). >> >> There are two things we can do: >> >> 1) Set it unconditionally in arch code (in a hook to be defined) >> 2) We remove it on a per-host bridge basis and ask for testing >> >> I agree this may have trickled from host bridge to host bridge through >> copy'n'paste and it is not based on any firmware assumtpion but I can't >> say if it is really needed. > > My basic position is that if resources are not assigned correctly, the > PCI core should automatically try to assign them, regardless of > whether PCI_REASSIGN_ALL_RSRC or PCI_REASSIGN_ALL_BUS is set. If that > doesn't work, I think there's something wrongin the PCI core and we > should fix that. > > This might be an opportunity to try removing the use of > pci_add_flags() and see what breaks. > > Bjorn > As per the Tegra TRM primary, secondary and subordinate default bus numbers are 0 and it is expecting SW to program these numbers. I believe this is the reason for adding PCI_REASSIGN_ALL_RSRC and PCI_REASSIGN_ALL_BUS flags. Looking at the function pci_scan_bridge_extend(), if secondary and subordinate bus numbers are 0 it is assigning bus numbers even if these flags are not set. In the basic testing with one endpoint PCIe link up is working fine without these flags, however I would like test with PCIe switch and multiple endpoints connected to Tegra. Manikanta
