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Message-ID: <20250801212725.GA3506354@bhelgaas>
Date: Fri, 1 Aug 2025 16:27:25 -0500
From: Bjorn Helgaas <helgaas@...nel.org>
To: Krishna Chaitanya Chundru <krishna.chundru@....qualcomm.com>
Cc: Bjorn Andersson <andersson@...nel.org>,
Konrad Dybcio <konradybcio@...nel.org>,
Rob Herring <robh@...nel.org>,
Krzysztof Kozlowski <krzk+dt@...nel.org>,
Conor Dooley <conor+dt@...nel.org>,
cros-qcom-dts-watchers@...omium.org,
Bjorn Helgaas <bhelgaas@...gle.com>,
"Rafael J. Wysocki" <rafael@...nel.org>,
Pavel Machek <pavel@...nel.org>, Len Brown <lenb@...nel.org>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
Danilo Krummrich <dakr@...nel.org>, linux-arm-msm@...r.kernel.org,
devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
linux-pci@...r.kernel.org, quic_vbadigan@...cinc.com,
quic_mrana@...cinc.com, sherry.sun@....com,
linux-pm@...r.kernel.org
Subject: Re: [PATCH v4 3/3] PCI: Add support for PCIe WAKE# interrupt
On Fri, Aug 01, 2025 at 04:29:44PM +0530, Krishna Chaitanya Chundru wrote:
> According to the PCIe specification 6, sec 5.3.3.2, there are two defined
> wakeup mechanisms: Beacon and WAKE# for the Link wakeup mechanisms to
> provide a means of signaling the platform to re-establish power and
> reference clocks to the components within its domain. Adding WAKE#
> support in PCI framework.
I think Beacon is a hardware mechanism invisible to software (PCIe
r7.0, sec 4.2.7.8.1).
> According to the PCIe specification, multiple WAKE# signals can exist in a
> system. In configurations involving a PCIe switch, each downstream port
> (DSP) of the switch may be connected to a separate WAKE# line, allowing
> each endpoint to signal WAKE# independently. To support this, the WAKE#
> should be described in the device tree node of the upstream bridge to which
> the endpoint is connected.
I think this says a bit more than we know. AFAICS, the PCIe spec does
not require any particular WAKE# routing. WAKE# *could* be routed to
an upstream bridge (as shown in the 5.3.3.2 implementation note), but
it doesn't have to be. I think we need to allow WAKE# to be described
by an Endpoint directly (which I think this patch does).
I'm not sure about searching upstream PCI bridges. I don't think
there's anything in the PCIe spec about a connection between WAKE#
routing and the PCI topology. Maybe we need to search enclosing DT
scopes? I'm not really sure how DT works in this respect. WAKE#
could be routed to some GPIO completely unrelated to the PCI host
bridge.
I don't see anything that would prevent a Switch Port from asserting a
WAKE# interrupt, so I'm not sure we should restrict it to Endpoints.
> For example, in a switch-based topology, the
> WAKE# can be defined in the DSP of the switch. In a direct connection
> scenario, the WAKE# can be defined in the root port. If all endpoints share
> a single WAKE# line, the GPIO should be defined in the root port.
>
> During endpoint probe, the driver searches for the WAKE# in its immediate
> upstream bridge. If not found, it continues walking up the hierarchy until
> it either finds a WAKE# or reaches the root port. Once found, the driver
> registers the wake IRQ in shared mode, as the WAKE# may be shared among
> multiple endpoints.
>
> When the IRQ is asserted, the wake handler triggers a pm_runtime_resume().
I guess "wake handler" refers to handle_threaded_wake_irq()? If so,
just use the name directly to make it easier for people to follow
this.
> The PM framework ensures that the parent device is resumed before the
> child i.e controller driver which can bring back link to D0.
Nit: a *device* can be in D0. Links would be in L0, etc.
> WAKE# is added in dts schema and merged based on this link.
>
> Link: https://lore.kernel.org/all/20250515090517.3506772-1-krishna.chundru@oss.qualcomm.com/
> Signed-off-by: Krishna Chaitanya Chundru <krishna.chundru@....qualcomm.com>
> ...
> +void pci_parse_of_wake_gpio(struct pci_dev *dev)
> +{
> + struct device_node *dn __free(device_node) = pci_device_to_OF_node(dev);
I'm still trying to wrap my head around __free(). Why are we using
__free() and no_free_ptr() here? AFAICS we're not allocating anything
here.
> + struct gpio_desc *gpio;
> +
> + if (!dn)
> + return;
> +
> + gpio = fwnode_gpiod_get_index(of_fwnode_handle(no_free_ptr(dn)),
> + "wake", 0, GPIOD_IN, NULL);
> + if (!IS_ERR(gpio))
> + dev->wake = gpio;
> +}
> +
> +void pci_remove_of_wake_gpio(struct pci_dev *dev)
> +{
> + if (!dev->wake)
> + return;
> +
> + gpiod_put(dev->wake);
> + dev->wake = NULL;
> +}
> #endif /* CONFIG_OF_IRQ */
>
> static int pci_parse_request_of_pci_ranges(struct device *dev,
> @@ -1010,3 +1035,44 @@ int of_pci_get_equalization_presets(struct device *dev,
> return 0;
> }
> EXPORT_SYMBOL_GPL(of_pci_get_equalization_presets);
> +
> +int pci_configure_wake_irq(struct pci_dev *pdev)
> +{
> + struct pci_dev *bridge = pdev;
> + struct gpio_desc *wake;
> + int ret, wake_irq;
> +
> + while (bridge) {
> + wake = bridge->wake;
> + if (wake)
> + break;
> + bridge = pci_upstream_bridge(bridge); // Move to upstream bridge
If we need to search more scopes, I think we should be searching DT
scopes, not PCI bridges.
> + }
> +
> + if (!wake)
> + return 0;
> +
> + wake_irq = gpiod_to_irq(wake);
> + if (wake_irq < 0) {
> + dev_err(&pdev->dev, "Failed to get wake irq: %d\n", wake_irq);
> + return wake_irq;
> + }
> +
> + device_init_wakeup(&pdev->dev, true);
> +
> + ret = dev_pm_set_dedicated_wake_irq_flags(&pdev->dev, wake_irq,
> + IRQF_SHARED | IRQ_TYPE_EDGE_FALLING);
> + if (ret < 0) {
> + dev_err(&pdev->dev, "Failed to set wake IRQ: %d\n", ret);
> + device_init_wakeup(&pdev->dev, false);
> + return ret;
> + }
> +
> + return 0;
> +}
> +
> +void pci_remove_wake_irq(struct pci_dev *pdev)
> +{
> + dev_pm_clear_wake_irq(&pdev->dev);
> + device_init_wakeup(&pdev->dev, false);
> +}
> diff --git a/drivers/pci/pci-driver.c b/drivers/pci/pci-driver.c
> index b853585cb1f87216981bde2a7782b8ed9c337636..2a1dca1d19b914d21b300ea78be0e0dce418cc88 100644
> --- a/drivers/pci/pci-driver.c
> +++ b/drivers/pci/pci-driver.c
> @@ -447,10 +447,19 @@ static int pci_device_probe(struct device *dev)
> if (error < 0)
> return error;
>
> + if (pci_pcie_type(pci_dev) == PCI_EXP_TYPE_ENDPOINT) {
I guess there's a policy question here: configuring this in
pci_device_probe() implies that we only pay attention to WAKE# when a
driver is bound to the device. Or, since WAKE# may be shared, I guess
we pay attention to it if any device sharing this WAKE# IRQ has a
driver?
And since we check for Endpoint, we ignore any potential WAKE# IRQs
from Switches?
ACPI has corresponding wakeup mechanisms. Are they limited to devices
with drivers or to Endpoints? Seems like this OF-based mechanism
should work similarly if possible.
> + error = pci_configure_wake_irq(pci_dev);
> + if (error) {
> + pcibios_free_irq(pci_dev);
As far as I can tell, pcibios_free_irq() is a no-op and I should have
removed it completely at the time of 6c777e8799a9 ("Revert "PCI, x86:
Implement pcibios_alloc_irq() and pcibios_free_irq()"").
I think we should remove it before this series rather than add new
calls.
> + return error;
> + }
> + }
> +
> pci_dev_get(pci_dev);
> error = __pci_device_probe(drv, pci_dev);
> if (error) {
> pcibios_free_irq(pci_dev);
> + pci_remove_wake_irq(pci_dev);
> pci_dev_put(pci_dev);
> }
>
> @@ -475,6 +484,7 @@ static void pci_device_remove(struct device *dev)
> pm_runtime_put_noidle(dev);
> }
> pcibios_free_irq(pci_dev);
> + pci_remove_wake_irq(pci_dev);
> pci_dev->driver = NULL;
> pci_iov_remove(pci_dev);
>
> diff --git a/drivers/pci/pci.h b/drivers/pci/pci.h
> index 12215ee72afb682b669c0e3a582b5379828e70c4..c8cf0b404a4f31b271f187dddd75a007c7566982 100644
> --- a/drivers/pci/pci.h
> +++ b/drivers/pci/pci.h
> @@ -920,6 +920,11 @@ void pci_release_of_node(struct pci_dev *dev);
> void pci_set_bus_of_node(struct pci_bus *bus);
> void pci_release_bus_of_node(struct pci_bus *bus);
>
> +void pci_parse_of_wake_gpio(struct pci_dev *dev);
> +void pci_remove_of_wake_gpio(struct pci_dev *dev);
> +int pci_configure_wake_irq(struct pci_dev *pdev);
> +void pci_remove_wake_irq(struct pci_dev *pdev);
> +
> int devm_of_pci_bridge_init(struct device *dev, struct pci_host_bridge *bridge);
> bool of_pci_supply_present(struct device_node *np);
> int of_pci_get_equalization_presets(struct device *dev,
> @@ -965,6 +970,11 @@ static inline int devm_of_pci_bridge_init(struct device *dev, struct pci_host_br
> return 0;
> }
>
> +static inline void pci_parse_of_wake_gpio(struct pci_dev *dev) { }
> +static inline void pci_remove_of_wake_gpio(struct pci_dev *dev) { }
> +static inline int pci_configure_wake_irq(struct pci_dev *pdev) { return 0; }
> +static inline void pci_remove_wake_irq(struct pci_dev *pdev) { }
> +
> static inline bool of_pci_supply_present(struct device_node *np)
> {
> return false;
> diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
> index e6a34db778266862564532becc2a30aec09bab22..4fb9d8df19bc41cb84dcd1886546076bcc867a43 100644
> --- a/drivers/pci/probe.c
> +++ b/drivers/pci/probe.c
> @@ -2717,6 +2717,8 @@ void pci_device_add(struct pci_dev *dev, struct pci_bus *bus)
> /* Set up MSI IRQ domain */
> pci_set_msi_domain(dev);
>
> + pci_parse_of_wake_gpio(dev);
> +
> /* Notifier could use PCI capabilities */
> ret = device_add(&dev->dev);
> WARN_ON(ret < 0);
> diff --git a/drivers/pci/remove.c b/drivers/pci/remove.c
> index 445afdfa6498edc88f1ef89df279af1419025495..1910f7c18b8f9b11c8136fea970788aaf834c97f 100644
> --- a/drivers/pci/remove.c
> +++ b/drivers/pci/remove.c
> @@ -52,6 +52,7 @@ static void pci_destroy_dev(struct pci_dev *dev)
> if (pci_dev_test_and_set_removed(dev))
> return;
>
> + pci_remove_of_wake_gpio(dev);
> pci_doe_sysfs_teardown(dev);
> pci_npem_remove(dev);
>
> diff --git a/include/linux/pci.h b/include/linux/pci.h
> index 05e68f35f39238f8b9ce08df97b384d1c1e89bbe..8f861298e41d2f0d2dd0fc3f5778fe0e77a93511 100644
> --- a/include/linux/pci.h
> +++ b/include/linux/pci.h
> @@ -548,6 +548,8 @@ struct pci_dev {
> /* These methods index pci_reset_fn_methods[] */
> u8 reset_methods[PCI_NUM_RESET_METHODS]; /* In priority order */
>
> + struct gpio_desc *wake; /* Holds WAKE# gpio */
> +
> #ifdef CONFIG_PCIE_TPH
> u16 tph_cap; /* TPH capability offset */
> u8 tph_mode; /* TPH mode */
>
> --
> 2.34.1
>
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