On Wed, 31 Jan 2024 16:50:32 +0000
Russell King (Oracle) [off-list ref] wrote:

From: James Morse <james.morse@arm.com>

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 is one that is marked as either enabled,
or online capable. Therefore, change acpi_gicc_is_usable() to check both
bits. However, we need to change the test in gic_acpi_match_gicc() back
to 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. Clear the
possible and present bits.

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.

When mapping redistributors found via GICC entries, handle the case
where the arch code believes the CPU is present and possible, but it
does not have an accessible redistributor. Print a warning and clear
the present and possible bits.

Signed-off-by: James Morse <james.morse@arm.com>
Signed-off-by: Russell King (Oracle) <redacted>

Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>



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