Re: [PATCH v2 2/2] PCI: hotplug: Add extension driver for Ampere Altra hotplug LED control

[Bjorn Helgaas]

On Fri, Sep 29, 2023 at 05:20:36PM -0700, D Scott Phillips wrote:
> On Ampere Altra, PCIe hotplug is handled through ACPI. A side interface is
> also present to request system firmware control of attention LEDs. Add an
> ACPI PCI Hotplug companion driver to support attention LED control.
> ...

> +	arm_smccc_smc(REQUEST, LED_CMD, led_status(status), LED_ATTENTION,
> +		      pci_domain_nr(bus) | (PCI_SLOT(root_port->devfn) << 4), 0, 0,

pci_domain_nr() returns "int" (normally 32 bits), but since this is an
ACPI system, the domain comes from _SEG, which is defined to be 16
bits (ACPI r6.5, sec 6.5.6).

So it looks like ORing in the "slot << 4" clobbers the upper 12 bits
of _SEG.

Is this code doing the right thing?