On 20 May 2016 at 10:40, Gabriele Paoloni <gabriele.paoloni@xxxxxxxxxx> wrote: > Hi Ard > >> -----Original Message----- >> From: Ard Biesheuvel [mailto:ard.biesheuvel@xxxxxxxxxx] [...] >> >> Is the PCIe root complex so special that you cannot simply describe an >> implementation that is not PNP0408 compatible as something else, under >> its own unique HID? If everybody is onboard with using ACPI, how is >> this any different from describing other parts of the platform >> topology? Even if the SBSA mandates generic PCI, they already deviated >> from that when they built the hardware, so pretending that it is a >> PNP0408 with quirks really does not buy us anything. > > From my understanding we want to avoid this as this would allow each > vendor to come up with his own code and it would be much more effort > for the PCI maintainer to rework the PCI framework to accommodate X86 > and "all" ARM64 Host Controllers... > > I guess this approach is too risky and we want to avoid this. Through > standardization we can more easily maintain the code and scale it to > multiple SoCs... > > So this is my understanding; maybe Jon, Tomasz or Lorenzo can give > a bit more explanation... > OK, so that boils down to recommending to vendors to represent known non-compliant hardware as compliant, just so that we don't have to change the code to support additional flavors of ECAM ? It's fine to be pragmatic, but that sucks. We keep confusing the x86 case with the ARM case here: for x86, they needed to deal with broken hardware *after* the fact, and all they could do is find /some/ distinguishing feature in order to guess which exact hardware they might be running on. For arm64, it is the opposite case. We are currently in a position where we can demand vendors to comply with the standards they endorsed themselves, and (ab)using ACPI + DMI as a de facto platform description rather than plain ACPI makes me think the DT crowd were actually right from the beginning. It *directly* violates the standardization principle, since it requires a priori knowledge inside the OS that a certain 'generic' device must be driven in a special way. So can anyone comment on the feasibility of adding support for devices with vendor specific HIDs (and no generic CIDs) to the current ACPI ECAM driver in Linux? -- 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
