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

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Message-ID: <20231026110418.GA1787436@bhelgaas>
Date:   Thu, 26 Oct 2023 06:04:18 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Anders Roxell <anders.roxell@...aro.org>
Cc:     D Scott Phillips <scott@...amperecomputing.com>,
        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, sfr@...b.auug.org.au,
        linux-next@...r.kernel.org
Subject: Re: [PATCH v2 2/2] PCI: hotplug: Add extension driver for Ampere
 Altra hotplug LED control

On Thu, Oct 26, 2023 at 12:47:31PM +0200, Anders Roxell wrote:
> On 2023-10-25 13:06, Bjorn Helgaas wrote:
> > 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;
> > +}
> 
> Hi,
> 
> Building todays linux-next tag next-20231026 for arm64 with
> CONFIG_HOTPLUG_PCI_ACPI_AMPERE_ALTRA=m I see the following build error.
> 
> drivers/pci/hotplug/acpiphp_ampere_altra.c: In function 'set_attention_status':
> drivers/pci/hotplug/acpiphp_ampere_altra.c:63:75: error: suggest parentheses around arithmetic in operand of '|' [-Werror=parentheses]
>    63 |                      PCI_SLOT(root_port->devfn) << 4 | pci_domain_nr(bus) & 0xf,
>       |                                                        ~~~~~~~~~~~~~~~~~~~^~~~~
> include/linux/arm-smccc.h:382:44: note: in definition of macro 'arm_smccc_smc'
>   382 | #define arm_smccc_smc(...) __arm_smccc_smc(__VA_ARGS__, NULL)
>       |                                            ^~~~~~~~~~~
> cc1: all warnings being treated as errors
> make[6]: *** [scripts/Makefile.build:243: drivers/pci/hotplug/acpiphp_ampere_altra.o] Error 1

My fault, fixed.

Bjorn