On Thu, Sep 22, 2016 at 01:44:46PM +0100, Lorenzo Pieralisi wrote: > On Thu, Sep 22, 2016 at 11:10:13AM +0000, Gabriele Paoloni wrote: > > Hi Lorenzo, Bjorn > > > > > -----Original Message----- > > > From: Lorenzo Pieralisi [mailto:lorenzo.pieralisi@xxxxxxx] > > > Sent: 22 September 2016 10:50 > > > To: Bjorn Helgaas > > > Cc: Ard Biesheuvel; Tomasz Nowicki; David Daney; Will Deacon; Catalin > > > Marinas; Rafael Wysocki; Arnd Bergmann; Hanjun Guo; Sinan Kaya; > > > Jayachandran C; Christopher Covington; Duc Dang; Robert Richter; Marcin > > > Wojtas; Liviu Dudau; Wangyijing; Mark Salter; linux- > > > pci@xxxxxxxxxxxxxxx; linux-arm-kernel@xxxxxxxxxxxxxxxxxxx; Linaro ACPI > > > Mailman List; Jon Masters; Andrea Gallo; Jeremy Linton; liudongdong > > > (C); Gabriele Paoloni; Jeff Hugo; linux-acpi@xxxxxxxxxxxxxxx; linux- > > > kernel@xxxxxxxxxxxxxxx; Rafael J. Wysocki > > > Subject: Re: [PATCH V6 3/5] PCI: thunder-pem: Allow to probe PEM- > > > specific register range for ACPI case > > > > > > On Wed, Sep 21, 2016 at 01:04:57PM -0500, Bjorn Helgaas wrote: > > > > On Wed, Sep 21, 2016 at 03:05:49PM +0100, Lorenzo Pieralisi wrote: > > > > > On Tue, Sep 20, 2016 at 02:17:44PM -0500, Bjorn Helgaas wrote: > > > > > > On Tue, Sep 20, 2016 at 04:09:25PM +0100, Ard Biesheuvel wrote: > > > > > > > > > > [...] > > > > > > > > > > > > None of these platforms can be fixed entirely in software, and > > > given > > > > > > > that we will not be adding quirks for new broken hardware, we > > > should > > > > > > > ask ourselves whether having two versions of a quirk, i.e., one > > > for > > > > > > > broken hardware + currently shipping firmware, and one for the > > > same > > > > > > > broken hardware with fixed firmware is really an improvement > > > over what > > > > > > > has been proposed here. > > > > > > > > > > > > We're talking about two completely different types of quirks: > > > > > > > > > > > > 1) MCFG quirks to use memory-mapped config space that doesn't > > > quite > > > > > > conform to the ECAM model in the PCIe spec, and > > > > > > > > > > > > 2) Some yet-to-be-determined method to describe address space > > > > > > consumed by a bridge. > > > > > > > > > > > > The first two patches of this series are a nice implementation > > > for 1). > > > > > > The third patch (ThunderX-specific) is one possibility for 2), > > > but I > > > > > > don't like it because there's no way for generic software like > > > the > > > > > > ACPI core to discover these resources. > > > > > > > > > > Ok, so basically this means that to implement (2) we need to assign > > > > > some sort of _HID to these quirky PCI bridges (so that we know what > > > > > device they represent and we can retrieve their _CRS). I take from > > > > > this discussion that the goal is to make sure that all non-config > > > > > resources have to be declared through _CRS device objects, which is > > > > > fine but that requires a FW update (unless we can fabricate ACPI > > > > > devices and corresponding _CRS in the kernel whenever we match a > > > > > given MCFG table signature). > > > > > > > > All resources consumed by ACPI devices should be declared through > > > > _CRS. If you want to fabricate ACPI devices or _CRS via kernel > > > > quirks, that's fine with me. This could be triggered via MCFG > > > > signature, DMI info, host bridge _HID, etc. > > > > > > I think the PNP quirk approach + PNP0c02 resource put forward by Gab > > > is enough. > > > > Great thanks as we take a final decision I will ask Dogndgong to submit > > another RFC based on this approach > > > > > > > > > > We discussed this already and I think we should make a decision: > > > > > > > > > > http://lists.infradead.org/pipermail/linux-arm-kernel/2016- > > > March/414722.html > > > > > > > > > > > > > I'd like to step back and come up with some understanding of > > > how > > > > > > > > non-broken firmware *should* deal with this issue. Then, if > > > we *do* > > > > > > > > work around this particular broken firmware in the kernel, it > > > would be > > > > > > > > nice to do it in a way that fits in with that understanding. > > > > > > > > > > > > > > > > For example, if a companion ACPI device is the preferred > > > solution, an > > > > > > > > ACPI quirk could fabricate a device with the required > > > resources. That > > > > > > > > would address the problem closer to the source and make it > > > more likely > > > > > > > > that the rest of the system will work correctly: /proc/iomem > > > could > > > > > > > > make sense, things that look at _CRS generically would work > > > (e.g, > > > > > > > > /sys/, an admittedly hypothetical "lsacpi", etc.) > > > > > > > > > > > > > > > > Hard-coding stuff in drivers is a point solution that doesn't > > > provide > > > > > > > > any guidance for future platforms and makes it likely that > > > the hack > > > > > > > > will get copied into even more drivers. > > > > > > > > > > > > > > > > > > > > > > OK, I see. But the guidance for future platforms should be 'do > > > not > > > > > > > rely on quirks', and what I am arguing here is that the more we > > > polish > > > > > > > up this code and make it clean and reusable, the more likely it > > > is > > > > > > > that will end up getting abused by new broken hardware that we > > > set out > > > > > > > to reject entirely in the first place. > > > > > > > > > > > > > > So of course, if the quirk involves claiming resources, let's > > > make > > > > > > > sure that this occurs in the cleanest and most compliant way > > > possible. > > > > > > > But any factoring/reuse concerns other than for the current > > > crop of > > > > > > > broken hardware should be avoided imo. > > > > > > > > > > > > If future hardware is completely ECAM-compliant and we don't need > > > any > > > > > > more MCFG quirks, that would be great. > > > > > > > > > > Yes. > > > > > > > > > > > But we'll still need to describe that memory-mapped config space > > > > > > somewhere. If that's done with PNP0C02 or similar devices (as is > > > done > > > > > > on my x86 laptop), we'd be all set. > > > > > > > > > > I am not sure I understand what you mean here. Are you referring > > > > > to MCFG regions reported as PNP0c02 resources through its _CRS ? > > > > > > > > Yes. PCI Firmware Spec r3.0, Table 4-2, note 2 says address ranges > > > > reported via MCFG or _CBA should be reserved by _CRS of a PNP0C02 > > > > device. > > > > > > Ok, that's agreed. It goes without saying that since you are quoting > > > the PCI spec, if FW fails to report MCFG regions in a PNP0c02 device > > > _CRS I will consider that a FW bug. > > > > > > > > IIUC PNP0C02 is a reservation mechanism, but it does not help us > > > > > associate its _CRS to a specific PCI host bridge instance, right ? > > > > > > > > Gab proposed a hierarchy that *would* associate a PNP0C02 device with > > > > a PCI bridge: > > > > > > > > Device (PCI1) { > > > > Name (_HID, "HISI0080") // PCI Express Root Bridge > > > > Name (_CID, "PNP0A03") // Compatible PCI Root Bridge > > > > Method (_CRS, 0, Serialized) { // Root complex resources > > > (windows) } > > > > Device (RES0) { > > > > Name (_HID, "HISI0081") // HiSi PCIe RC config base address > > > > Name (_CID, "PNP0C02") // Motherboard reserved resource > > > > Name (_CRS, ResourceTemplate () { ... } > > > > } > > > > } > > > > > > > > That's a possibility. The PCI Firmware Spec suggests putting RES0 at > > > > the root (under \_SB), but I don't know why. > > > > > > > > Putting it at the root means we couldn't generically associate it > > > with > > > > a bridge, although I could imagine something like this: > > > > > > > > Device (RES1) { > > > > Name (_HID, "HISI0081") // HiSi PCIe RC config base address > > > > Name (_CID, "PNP0C02") // Motherboard reserved resource > > > > Name (_CRS, ResourceTemplate () { ... } > > > > Method (BRDG) { "PCI1" } // hand-wavy ASL > > > > } > > > > Device (PCI1) { > > > > Name (_HID, "HISI0080") // PCI Express Root Bridge > > > > Name (_CID, "PNP0A03") // Compatible PCI Root Bridge > > > > Method (_CRS, 0, Serialized) { // Root complex resources > > > (windows) } > > > > } > > > > > > > > Where you could search PNP0C02 devices for a cookie that matched the > > > > host bridge.o > > > > > > Ok, I am fine with both and I think we are converging, but the way > > > to solve this problem has to be uniform for all ARM partners (and > > > not only ARM). Two points here: > > > > > > 1) Adding a device/subdevice allows people to add a _CRS reporting the > > > non-window bridge resources. Fine. It also allows people to chuck in > > > there all sorts of _DSD properties to describe their PCI host bridge > > > as it is done with DT properties (those _DSD can contain eg clocks > > > etc.), this may be tempting (so that they can reuse the same DT > > > driver and do not have to update their firmware) but I want to be > > > clear here: that must not happen. So, a subdevice with a _CRS to > > > report resources, yes, but it will stop there. > > > 2) It is unclear to me how to formalize the above. People should not > > > write FW by reading the PCI mailing list, so these guidelines have > > > to > > > be written, somehow. I do not want to standardize quirks, I want > > > to prevent random ACPI table content, which is different. > > > Should I report this to the ACPI spec working group ? If we do > > > not do that everyone will go solve this problem as they deem fit. > > > > > > > Do we really need to formalize this? > > > > As we discussed in the Linaro call at the moment we have few vendors > > that need quirks and we want to avoid promoting/accepting quirks for > > the future. > > > > At the time of the call I think we decided to informally accept a set > > of quirks for the current platforms and reject any other quirk coming > > after a certain date/kernel version (this to be decided). > > > > I am not sure if there is a way to document/formalize a temporary > > exception from the rule... > > - (1) will be enforced. I'm not sure it's necessary or possible to enforce a "no future quirks" rule. For one thing, there's already a pretty strong incentive to avoid quirks: if your hardware doesn't require quirks, it works with OSes already in the field. MCFG quirks allow us to use the generic ACPI pci_root.c driver even if the hardware doesn't support ECAM quite according to the spec. PNP0C02 usage is a workaround for the failure of the Consumer/Producer bit. PNP0C02 quirks compensate for firmware that doesn't describe resource usage accurately. It's possible the ACPI spec folks could come up with a better Consumer/Producer workaround, if that's needed. Apparently x86 hasn't needed it yet. If people add _DSD methods for clocks or whatnot, the hardware won't work with the generic pci_root.c driver, so there's already an incentive for avoiding them. x86 has managed without such methods; arm64 should be able to do the same. > - We do not know whether PNP0c02 can be used in non-root devices _CRS > - Are we sure (given that we are implementing this to make sure we are > able to validate resources) that it is valid to have a subdevice with > a _CRS whose resources are not contained in its parent _CRS address > space (because that's exactly the case for these quirks) ? > > That's what I mean by formalizing, I want to know how PNP0c02 should > be used. We all want platforms with quirks to be enabled asap but only > if we stick to the ACPI specifications. On top of that, with the > bindings above, the kernel would end up creating a platform device for > the "fake" device with a _CRS approach, which is questionable. > > > [...] > > > > > > > > For FW that is immutable I really do not see what we can do apart > > > > > from hardcoding the non-config resources (consumed by a bridge), > > > > > somehow. > > > > > > > > Right. Well, I assume you mean we should hard-code "non-window > > > > resources consumed directly by a bridge". If firmware in the field > > > is > > > > broken, we should work around it, and that may mean hard-coding some > > > > resources. > > > > > > > > My point is that the hard-coding should not be buried in a driver > > > > where it's invisible to the rest of the kernel. If we hard-code it > > > in > > > > a quirk that adds _CRS entries, then the kernel will work just like > > > it > > > > would if the firmware had been correct in the first place. The > > > > resource will appear in /sys/devices/pnp*/*/resources and > > > /proc/iomem, > > > > and if we ever used _SRS to assign or move ACPI devices, we would > > > know > > > > to avoid the bridge resource. > > > > > > We are in complete agreement here. > > > > > > Thanks, > > > Lorenzo > > -- To unsubscribe from this list: send the line "unsubscribe linux-acpi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
