On Wed, 29 May 2024 14:34:41 +0100, Jonathan Cameron <Jonathan.Cameron@xxxxxxxxxx> wrote: > > From: James Morse <james.morse@xxxxxxx> > > To support virtual CPU hotplug, ACPI has added an 'online capable' bit > to the MADT GICC entries. This indicates a disabled CPU entry may not > be possible to online via PSCI until firmware has set enabled bit in > _STA. > > This means that a "usable" GIC redistributor is one that is marked as > either enabled, or online capable. The meaning of the > acpi_gicc_is_usable() would become less clear than just checking the > pair of flags at call sites. As such, drop that helper function. > The test in gic_acpi_match_gicc() remains as testing just the > enabled bit so the count of enabled distributors is correct. > > What about the redistributor in the GICC entry? ACPI doesn't want to say. > Assume the worst: When a redistributor is described in the GICC entry, > but the entry is marked as disabled at boot, assume the redistributor > is inaccessible. > > The GICv3 driver doesn't support late online of redistributors, so this > means the corresponding CPU can't be brought online either. > Rather than modifying cpu masks that may already have been used, > register a new cpuhp callback to fail this case. This must run earlier > than the main gic_starting_cpu() so that this case can be rejected > before the section of cpuhp that runs on the CPU that is coming up as > that is not allowed to fail. This solution keeps the handling of this > broken firmware corner case local to the GIC driver. As precise ordering > of this callback doesn't need to be controlled as long as it is > in that initial prepare phase, use CPUHP_BP_PREPARE_DYN. > > Systems that want CPU hotplug in a VM can ensure their redistributors > are always-on, and describe them that way with a GICR entry in the MADT. > > Suggested-by: Marc Zyngier <maz@xxxxxxxxxx> > Signed-off-by: James Morse <james.morse@xxxxxxx> > Signed-off-by: Russell King (Oracle) <rmk+kernel@xxxxxxxxxxxxxxx> > Tested-by: Miguel Luis <miguel.luis@xxxxxxxxxx> > Co-developed-by: Jonathan Cameron <Jonathan.Cameron@xxxxxxxxxx> > Signed-off-by: Jonathan Cameron <Jonathan.Cameron@xxxxxxxxxx> Acked-by: Marc Zyngier <maz@xxxxxxxxxx> M. -- Without deviation from the norm, progress is not possible.
