On Mon, Jan 20, 2020 at 12:10:42PM +0100, Thierry Reding wrote: [...] > > > Currently the BSP has the kernel booting through Device Tree mechanism > > > and there is a plan to support UEFI based boot as well in the future software > > > releases for which we need this quirky way of handling ECAM. > > > Tegra194 is going to be the only and last chip with this issue and next chip > > > in line in Tegra SoC series will be fully compliant with ECAM. > > > > ACPI on ARM64 works on a standard subset of systems, defined by the > > ARM SBSA: > > > > http://infocenter.arm.com/help/topic/com.arm.doc.den0029c/Server_Base_System_Architecture_v6_0_ARM_DEN_0029C_SBSA_6_0.pdf > > I don't understand what you're saying here. Are you saying that you want > to prevent vendors from upstreaming code that they need to support their > ACPI based platforms? I understand that the lack of support for proper > ECAM means that a platform will not be SBSA compatible, but I wasn't > aware that lack of SBSA compatibility meant that a platform would be > prohibited from implementing ACPI support in an upstream kernel. ACPI on ARM64 requires a set of HW components described in the SBSA. If those HW requirements are not fulfilled you can't bootstrap an ARM64 system with ACPI - it is as simple as that. It is not even appropriate to discuss this on a Linux mailing list anymore since it is HW requirements and it has been public information since ACPI on ARM64 was first enabled. > > These patches will have to be carried out of tree, the MCFG quirk > > mechanism (merged as Bjorn said more than three years ago) was supposed > > to be a temporary plaster to bootstrap server platforms with teething > > issues, the aim is to remove it eventually not to add more code to it > > indefinitely. > > Now, I fully agree that quirks are suboptimal and we'd all prefer if we > didn't have to deal with them. Unfortunately the reality is that > mistakes happen and hardware doesn't always work the way we want it to. > There's plenty of other quirk mechanisms in the kernel, and frankly this > one isn't really that bad in comparison. Because you don't have to maintain it ;) - I think I said what I had to say about the MCFG mechanism in the past - it has been three years and counting - it is time to remove it rather that adding to it. > > So I am afraid but this quirk (and any other coming our way) will not be > > merged in an upstream kernel anymore - for any queries please put Nvidia > > in touch. > > Again, I don't understand what you're trying to achieve here. You seem > to be saying that we categorically can't support this hardware because > it isn't fully SBSA compatible. I am not trying to achieve anything - I am just stating public information - let me repeat it again for interested readers: to bootstrap an ARM64 system with ACPI the platform HW design must follow the SBSA guidelines. > Do you have any alternative suggestions on how we can support this in an > upstream kernel? Booting with a device tree ? > We realized a while ago that we cannot achieve proper ECAM on Tegra194 > because of some issues with the hardware and we've provided this as > feedback to the hardware engineers. As a result, the next generation of > Tegra should no longer suffer from these issues. We will bootstrap next generation Tegra with ACPI then, there are SBSA tests available for compliancy - again, that's a matter for Nvidia and Arm to settle, not a mailing list discussion. > As for Tegra194, that chip taped out two years ago and it isn't possible > to make it fully ECAM compliant other than by revising the chip, which, > frankly, isn't going to happen. > > So I see two options here: either we find a way of dealing with this, by > either merging this quirk or finding an alternative solution, or we make > the decision that some hardware just can't be supported. > > The former is fairly common, whereas I've never heard of the latter. What does this mean ? Should I wreck the upstream kernel to make it boot with ACPI on *any* ARM64 platform out there then ? My stance is clear above and the ACPI PCI programming model - inclusive of firmware - has been there since ACPI was deployed, if ACPI support is required HW must comply, either that or it is out of tree patches and I can't be blamed for that. Thanks, Lorenzo
