Hi Bjorn > -----Original Message----- > From: Bjorn Helgaas [mailto:helgaas@xxxxxxxxxx] > Sent: 21 April 2016 16:49 > To: Gabriele Paoloni > Cc: Jisheng Zhang; jingoohan1@xxxxxxxxx; pratyush.anand@xxxxxxxxx; > bhelgaas@xxxxxxxxxx; linux-pci@xxxxxxxxxxxxxxx; linux- > kernel@xxxxxxxxxxxxxxx; linux-arm-kernel@xxxxxxxxxxxxxxxxxxx > Subject: Re: [PATCH v2] PCI: designware: move remaining rc setup code > to dw_pcie_setup_rc() > > On Tue, Apr 12, 2016 at 09:43:32AM +0000, Gabriele Paoloni wrote: > > Hi Bjorn > > > > [...] > > > > > > > > > > > > What's the hisi plan for resuming after suspend-to-RAM? How > does > > > the > > > > > RC get reprogrammed after it loses all its state? > > > > > > > > PM is not part of the driver yet. This is planned for near > > > > future release so haven't made such considerations yet > > > > > > > > > > What would break if hisi did call dw_pcie_setup_rc()? I know > you > > > said > > > > > it would overwrite what the bootloader already did, which is > true. > > > > > > > > I am try to figure this out now with our HW team. > > > > > > > > > > > > > > But hisi does call dw_pcie_host_init(), so it reads pp->mem > (which > > > > > determines pp->mem_base) and pp->lanes from the DT. Other > drivers > > > > > then call dw_pcie_setup_rc() which programs the RC based on > > > > > pp->mem_base and pp->lanes. So hisi assumes UEFI programmed > the RC > > > to > > > > > match the DT, while the other drivers read the DT and program > the > > > RC > > > > > to match. The latter seems more robust because it enforces the > > > > > consistency rather than relying on it. > > > > > > > > Yes I agree with you, however we have preferred to move RC config > to > > > > BIOS to have a single driver to support multiple versions of the > > > > same SoC. > > > > > > I think there are two reasonable approaches: > > > > > > 1) A single generic driver that doesn't have any knowledge about > the > > > chipset registers; it uses run-time firmware interfaces to manage > > > the bridge. The ACPI pci_root.c driver is the best example so > far > > > and works very well. It supports basically all x86 and ia64 > > > chipsets and requires no kernel work for new ones. > > > > > > 2) Native drivers specific to each chipset. These may get > > > configuration information from DT, but they do their own > > > register-level programming of the device without run-time help > from > > > firmware. > > > > > > I think hisi is a native driver because it uses hip05/hip06 > registers > > > to check link state and perform config operations. And apparently > you > > > rely on the ATU, BAR, class, and link width programming currently > done > > > in dw_pcie_host_init(). But you want to rely on pre-boot firmware > to > > > set up the link. That doesn't make sense to me -- if the driver > wants > > > to twiddle the registers, it should know how to do it all. I don't > > > see how you can reasonably manage this half-way approach. > > > > > > > The patch I proposed above does the same job as the original > patch > > > > proposed by Jisheng and also allows hisi driver to call the moved > > > > code. > > > > > > > > Do you see anything wrong with it? > > > > > > Only that it makes the structure more complicated and we haven't > > > identified a corresponding benefit yet. > > > > Finally I have checked that assigning .host_init function pointer > > in our driver to call dw_pcie_setup_rc() will not affect the values > > already set by BIOS. > > > > Also I agree with you that a hybrid approach is not ideal. > > > > So I will update the driver to call dw_pcie_setup_rc() from > > .host_init and ask the BIOS team to update the firmware for next > > releases (the driver will be backward compatible anyway). > > Am I right in assuming that the patch currently in my tree: > > https://git.kernel.org/cgit/linux/kernel/git/helgaas/pci.git/commit/?h= > pci/host-designware&id=1488aefa37a4033080942c860294d13c613ec829 > > will work for you? I'm going to assume so unless I hear otherwise. Yes you are right. I thought it was clear by the last conclusion. Sorry if it was not explicit. Many Thanks and Regards Gab > > Bjorn -- 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
