A big +1 to the below :) :) :) -- Computer Architect | Sent from my 64-bit #ARM Powered phone > On May 24, 2016, at 13:24, Lorenzo Pieralisi <lorenzo.pieralisi@xxxxxxx> wrote: > > Hi Bjorn, > > On Mon, May 23, 2016 at 06:39:18PM -0500, Bjorn Helgaas wrote: > > [...] > >> On Mon, May 23, 2016 at 03:16:01PM +0000, Gabriele Paoloni wrote: >> I don't think of ECAM support itself as a "driver". It's just a >> service available to drivers, similar to OF resource parsing. >> >> Per PCI Firmware r3.2, sec 4.1.5, "PNP0A03" means a PCI/PCI-X/PCIe >> host bridge. "PNP0A08" means a PCI-X Mode 2 or PCIe bridge that >> supports extended config space. It doesn't specify how we access that >> config space, so I think hardware with non-standard ECAM should still >> have PNP0A03 and PNP0A08 in _CID or _HID. >> >> "ECAM" as used in the specs (PCIe r3.0, sec 7.2.2, and PCI Firmware >> r3.2, sec 4.1) means: >> >> (a) a memory-mapped model for config space access, and >> (b) a specific mapping of address bits to bus/device/function/ >> register >> >> MCFG and _CBA assume both (a) and (b), so I think a device with >> non-standard ECAM mappings should not be described in MCFG or _CBA. >> >> If a bridge has ECAM with non-standard mappings, I think either a >> vendor-specific _HID or a device-specific method, e.g., _DSM, could >> communicate that. >> >> Jon, I agree that we should avoid describing non-standardized hardware >> in Linux-specific ways. Is there a mechanism in use already? How >> does Windows handle this? DMI is a poor long-term solution because it >> requires ongoing maintenance for new platforms, but I think it's OK >> for getting started with platforms already shipping. >> >> A _DSM has the advantage that once it is defined and supported, OEMs >> can ship new platforms without requiring a new quirk or a new _HID to >> be added to a driver. >> >> There would still be the problem of config access before the namespace >> is available, i.e., the MCFG use case. I don't know how important >> that is. Defining an MCFG extension seems like the most obvious >> solution. > > Your summary above is a perfect representation of the situation. > > We had an opportunity to sync-up on the current status of ACPI PCI > for ARM64 (and talked about a way forward for this series, which > includes quirks handling), let me summarize it here for everyone > involved so that we can agree on a way forward. > > 1) ACPI PCI support for PNP0A03/PNP0A08 host bridges on top of MCFG > ECAM for config space is basically ready (Tomasz and JC addressed > Rafael's concerns in relation to ARM64 specific code, and managed > to find a way to allocate domain numbers in preparation for Arnd > pci_create_root_bus() clean-up, v8 to be posted shortly and should > be final). This provides support for de-facto ACPI/PCI ECAM base > standard for ARM64 (with a clean-split between generic code and ARM64 > bits, where ARM64, like X86 and IA64, manages in arch code IO space and > PCI resources, to be further consolidated in the near future). > I do not think anyone can complain about the generality of what we > achieved, for systems that are PCI standard (yes, PCI STANDARD) this > would just be sufficient. > 2) In a real world (1) is not enough. Some ARM64 platforms, not entirely > ECAM compliant, already shipped with the corresponding firmware that > we can't update. HW has ECAM quirks and to work around it in the kernel > we put forward many solutions to the problem, it is time we found a > solution (when, of course, (1) is completed and upstream). > Using the MCFG table OEMID matching floated around in this thread > would work fine for most of the platforms (and cross-OS) that have > shipped with HW ECAM quirks, so I think that's the starting point for > our solution and that's how we can sort this out, _today_. > > The solution is a trivial look-up table: > MCFG OEMID <-> PCI config space ops > > 3) (2) does not just work on some platforms (and we can't predict the > future either - actually I can, it is three letters, ECAM), simply > because MCFG OEMID matching does not provide a way to attach further > data to the MCFG (eg if config space for, say, bus 0 domain 0, is not > ECAM compliant, the config region can't be handled and must not be > handled through a corresponding MCFG region. > That's the problem Gabriele is facing and wants to solve through > something like: > > https://lkml.org/lkml/2016/3/9/91 > > in the respective ACPI tables-bindings. It may be an idea worth > pursuing, it does not solve (2) simply because that FW has shipped, > we can't patch it any longer. > > Hence to finally support ACPI PCI on ARM64 I suggest we carry out the > following steps, in order: > > - Let's complete/merge (1), that's fundamental to this whole thread > - On top of (1) we apply a quirking mechanism based on (2) that allows > us to boot mainline with boxes shipping today with no FW update required. > - We devise a way to handle quirks that is more generic than (2) so that > can we can accomodate further platforms that can't rely on (2) but > have more leeway in terms of FW updates. > > I hope that's a reasonable plan, Tomasz's v8 series coming to kick it off. > > Thank you, > Lorenzo -- 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
