On Mon, Jan 22, 2024 at 05:22:46PM +0100, Rafael J. Wysocki wrote: > On Mon, Jan 22, 2024 at 5:02 PM Jonathan Cameron > <Jonathan.Cameron@xxxxxxxxxx> wrote: > > > > On Mon, 15 Jan 2024 11:06:29 +0000 > > "Russell King (Oracle)" <linux@xxxxxxxxxxxxxxx> wrote: > > > > > On Mon, Dec 18, 2023 at 09:22:03PM +0100, Rafael J. Wysocki wrote: > > > > On Wed, Dec 13, 2023 at 1:49 PM Russell King <rmk+kernel@xxxxxxxxxxxxxxx> wrote: > > > > > > > > > > From: James Morse <james.morse@xxxxxxx> > > > > > > > > > > ACPI has two descriptions of CPUs, one in the MADT/APIC table, the other > > > > > in the DSDT. Both are required. (ACPI 6.5's 8.4 "Declaring Processors" > > > > > says "Each processor in the system must be declared in the ACPI > > > > > namespace"). Having two descriptions allows firmware authors to get > > > > > this wrong. > > > > > > > > > > If CPUs are described in the MADT/APIC, they will be brought online > > > > > early during boot. Once the register_cpu() calls are moved to ACPI, > > > > > they will be based on the DSDT description of the CPUs. When CPUs are > > > > > missing from the DSDT description, they will end up online, but not > > > > > registered. > > > > > > > > > > Add a helper that runs after acpi_init() has completed to register > > > > > CPUs that are online, but weren't found in the DSDT. Any CPU that > > > > > is registered by this code triggers a firmware-bug warning and kernel > > > > > taint. > > > > > > > > > > Qemu TCG only describes the first CPU in the DSDT, unless cpu-hotplug > > > > > is configured. > > > > > > > > So why is this a kernel problem? > > > > > > So what are you proposing should be the behaviour here? What this > > > statement seems to be saying is that QEMU as it exists today only > > > describes the first CPU in DSDT. > > > > This confuses me somewhat, because I'm far from sure which machines this > > is true for in QEMU. I'm guessing it's a legacy thing with > > some old distro version of QEMU - so we'll have to paper over it anyway > > but for current QEMU I'm not sure it's true. > > > > Helpfully there are a bunch of ACPI table tests so I've been checking > > through all the multi CPU cases. > > > > CPU hotplug not enabled. > > pc/DSDT.dimmpxm - 4x Processor entries. -smp 4 > > pc/DSDT.acpihmat - 2x Processor entries. -smp 2 > > q35/DSDT.acpihmat - 2x Processor entries. -smp 2 > > virt/DSDT.acpihmatvirt - 4x ACPI0007 entries -smp 4 > > q35/DSDT.acpihmat-noinitiator - 4 x Processor () entries -smp 4 > > virt/DSDT.topology - 8x ACPI0007 entries > > > > I've also looked at the code and we have various types of > > CPU hotplug on x86 but they all build appropriate numbers of > > Processor() entries in DSDT. > > Arm likewise seems to build the right number of ACPI0007 entries > > (and doesn't yet have CPU HP support). > > > > If anyone can add a reference on why this is needed that would be very > > helpful. > > Yes, it would. > > Personally, I would prefer to assume that it is not necessary until it > turns out that (1) there is firmware with this issue actually in use > and (2) updating the firmware in question to follow the specification > is not practical. > > Otherwise, we'd make it easier to ship non-compliant firmware for no > good reason. If Salil can't come up with a reason, then I'm in favour of dropping the patch like already done for patch 2. If the code change serves no useful purpose, there's no point in making the change. -- RMK's Patch system: https://www.armlinux.org.uk/developer/patches/ FTTP is here! 80Mbps down 10Mbps up. Decent connectivity at last!
