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

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Date:   Wed, 25 Oct 2023 13:06:27 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     D Scott Phillips <scott@...amperecomputing.com>
Cc:     linux-acpi@...r.kernel.org, linux-pci@...r.kernel.org,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        linux-kernel@...r.kernel.org, Len Brown <lenb@...nel.org>,
        Darren Hart <darren@...amperecomputing.com>,
        patches@...erecomputing.com
Subject: Re: [PATCH v2 2/2] PCI: hotplug: Add extension driver for Ampere
 Altra hotplug LED control

On Wed, Oct 25, 2023 at 10:41:46AM -0700, D Scott Phillips wrote:
> Bjorn Helgaas <helgaas@...nel.org> writes:
> 
> > 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?
> 
> Hi Bjorn,
> 
> on these Altra platforms _SEG is limited within 0-11. I can add an `&
> 0xf` to pci_domain_nr() to make it clear that the segment number is
> encoded down into 4 bits in the smc request.

If the following looks OK, we're all set.  I put these on pci/hotplug
for v6.7, thanks!

+static int set_attention_status(struct hotplug_slot *slot, u8 status)
+{
+	struct arm_smccc_res res;
+	struct pci_bus *bus;
+	struct pci_dev *root_port;
+	unsigned long flags;
+	u32 handle;
+	int ret = 0;
+
+	bus = slot->pci_slot->bus;
+	root_port = pcie_find_root_port(bus->self);
+	if (!root_port)
+		return -ENODEV;
+
+	local_irq_save(flags);
+	arm_smccc_smc(HANDLE_OPEN, led_service_id[0], led_service_id[1],
+		      led_service_id[2], led_service_id[3], 0, 0, 0, &res);
+	if (res.a0) {
+		ret = -ENODEV;
+		goto out;
+	}
+	handle = res.a1 & 0xffff0000;
+
+	arm_smccc_smc(REQUEST, LED_CMD, led_status(status), LED_ATTENTION,
+		     PCI_SLOT(root_port->devfn) << 4 | pci_domain_nr(bus) & 0xf,
+		     0, 0, handle, &res);
+	if (res.a0)
+		ret = -ENODEV;
+
+	arm_smccc_smc(HANDLE_CLOSE, handle, 0, 0, 0, 0, 0, 0, &res);
+
+ out:
+	local_irq_restore(flags);
+	return ret;
+}