Re: [RFC PATCH V2] acpi/irq: Add stacked IRQ domain support to PCI interrupt link

[Bjorn Helgaas <helgaas@kernel.org>]

Nit: please don't just make up random styles for the subject.  Run
"git log --oneline" on the file and/or the directory and try to follow
the existing convention.  Using random styles adds noise to the
system.

On Tue, Nov 17, 2020 at 09:42:14PM +0800, Chen Baozi wrote:
> Some PCIe designs require software to do extra acknowledgements for
> legacy INTx interrupts. If the driver is written only for device tree,
> things are simple. In that case, a new driver can be written under
> driver/pci/controller/ with a DT node of PCIe host written like:
> 
>   pcie {
>     ...
>     interrupt-map = <0 0 0  1  &pcie_intc 0>,
>                     <0 0 0  2  &pcie_intc 1>,
>                     <0 0 0  3  &pcie_intc 2>,
>                     <0 0 0  4  &pcie_intc 3>;
> 
>     pcie_intc: legacy-interrupt-controller {
>       interrupt-controller;
>       #interrupt-cells = <1>;
>       interrupt-parent = <&gic>;
>       interrupts = <0 226 4>;
>     };
>   };
> 
> Similar designs can be found on Aardvark, MediaTek Gen2 and Socionext
> UniPhier PCIe controller at the moment. Essentially, those designs are
> supported by inserting an extra interrupt controller between PCIe host
> and GIC and parse the topology in a DT-based PCI controller driver.

If I understand correctly, we previously ignored the Resource Source
field of an Extended Interrupt Descriptor in the _PRS method of
PNP0C0F PCI Interrupt Link devices, and this patch adds support for
it.

If that's true, this has nothing to do with DT, other than DT being
another way to describe the same topology, and the above details
really aren't relevant to this patch.

> As we turn to ACPI, All the PCIe hosts are described the same ID of
> "PNP0A03" and share driver/acpi/pci_root.c. It comes to be a problem
> to make this kind of PCI INTx work under ACPI.

s/All the PCIe/all the PCIe/

But this paragraph should probably just go away in favor of something
about implementing Resource Source support.

> Therefore, we introduce an stacked IRQ domain support to PCI interrupt
> link for ACPI. With this support, we can populate the ResourceSource
> to refer to a device object that describes an interrupt controller.
> That would allow us to refer to a dedicated driver which implements
> the logic needed to manage the interrupt state. With this patch,
> those PCI interrupt links can be supported by describing the INTx
> in ACPI table as the following example:

"Stacked IRQ domain" sounds like a detail of how you're implementing
support for the Resource Source field for PCI Interrupt Links.

I don't know what the dedicated driver refers to.  This *should* be
all generic code the follows the ACPI spec (which is pretty sketchy in
this area).  But I assume that there's no special driver needed for
devices like \SB.IXIU, and the logic associated with the interrupt
controller is in the AML associated with IXIU.  It would probably be
useful to mention the relevant methods in the IXIU methods in the
example below.

From ACPI v6.3, Table 6-200, it looks like this patch should include
changes to acpi_bus_osc_support() to advertise "Interrupt
ResourceSource support".

>   Device (IXIU) {
>     ...
>   }
> 
>   Device(LINKA) {
>     Name(_HID, EISAID("PNP0C0F"))
>     Name(_PRS, ResourceTemplate(){
>       Interrupt(ResourceProducer, Level, ActiveHigh, Exclusive, 0, "\\SB.IXIU")
>         { 60 }
>     })
>     ...
>   }
> 
>   Device(PCI0) {
>     ...
>     Name(_PRT, Package{
>       Package{ 0x0000FFFF, 0, LINKA, 0 }
>       ...
>     })
>   }
> 
> Signed-off-by: Chen Baozi <chenbaozi@phytium.com.cn>
> ---
>  drivers/acpi/irq.c          | 22 +++++++++++++++++++++-
>  drivers/acpi/pci_irq.c      |  6 ++++--
>  drivers/acpi/pci_link.c     | 17 +++++++++++++++--
>  include/acpi/acpi_drivers.h |  2 +-
>  include/linux/acpi.h        |  4 ++++
>  5 files changed, 45 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/acpi/irq.c b/drivers/acpi/irq.c
> index e209081d644b..e78a44815c44 100644
> --- a/drivers/acpi/irq.c
> +++ b/drivers/acpi/irq.c
> @@ -81,6 +81,25 @@ void acpi_unregister_gsi(u32 gsi)
>  }
>  EXPORT_SYMBOL_GPL(acpi_unregister_gsi);
>  
> +int acpi_register_irq(struct device *dev, u32 irq, int trigger,
> +		      int polarity, struct fwnode_handle *domain_id)
> +{
> +	struct irq_fwspec fwspec;
> +
> +	if (WARN_ON(!domain_id)) {
> +		pr_warn("GSI: No registered irqchip, giving up\n");

This message could contain more information, e.g., by using
dev_warn(), including the irq value, etc.

> +		return -EINVAL;
> +	}
> +
> +	fwspec.fwnode = domain_id;
> +	fwspec.param[0] = irq;
> +	fwspec.param[1] = acpi_dev_get_irq_type(trigger, polarity);
> +	fwspec.param_count = 2;
> +
> +	return irq_create_fwspec_mapping(&fwspec);
> +}
> +EXPORT_SYMBOL_GPL(acpi_register_irq);

Why does this need to be exported?  You only call it from
acpi_pci_irq_enable(), which cannot be a module.

>  /**
>   * acpi_get_irq_source_fwhandle() - Retrieve fwhandle from IRQ resource source.
>   * @source: acpi_resource_source to use for the lookup.
> @@ -92,7 +111,7 @@ EXPORT_SYMBOL_GPL(acpi_unregister_gsi);
>   * Return:
>   * The referenced device fwhandle or NULL on failure
>   */
> -static struct fwnode_handle *
> +struct fwnode_handle *
>  acpi_get_irq_source_fwhandle(const struct acpi_resource_source *source)
>  {
>  	struct fwnode_handle *result;
> @@ -115,6 +134,7 @@ acpi_get_irq_source_fwhandle(const struct acpi_resource_source *source)
>  	acpi_bus_put_acpi_device(device);
>  	return result;
>  }
> +EXPORT_SYMBOL_GPL(acpi_get_irq_source_fwhandle);

This doesn't look like it needs to be exported either.

>  /*
>   * Context for the resource walk used to lookup IRQ resources.
> diff --git a/drivers/acpi/pci_irq.c b/drivers/acpi/pci_irq.c
> index 14ee631cb7cf..19296d70c95c 100644
> --- a/drivers/acpi/pci_irq.c
> +++ b/drivers/acpi/pci_irq.c
> @@ -410,6 +410,7 @@ int acpi_pci_irq_enable(struct pci_dev *dev)
>  	char *link = NULL;
>  	char link_desc[16];
>  	int rc;
> +	struct fwnode_handle *irq_domain;
>  
>  	pin = dev->pin;
>  	if (!pin) {
> @@ -438,7 +439,8 @@ int acpi_pci_irq_enable(struct pci_dev *dev)
>  			gsi = acpi_pci_link_allocate_irq(entry->link,
>  							 entry->index,
>  							 &triggering, &polarity,
> -							 &link);
> +							 &link,
> +							 &irq_domain);
>  		else
>  			gsi = entry->index;
>  	} else
> @@ -462,7 +464,7 @@ int acpi_pci_irq_enable(struct pci_dev *dev)
>  		return 0;
>  	}
>  
> -	rc = acpi_register_gsi(&dev->dev, gsi, triggering, polarity);
> +	rc = acpi_register_irq(&dev->dev, gsi, triggering, polarity, irq_domain);
>  	if (rc < 0) {
>  		dev_warn(&dev->dev, "PCI INT %c: failed to register GSI\n",
>  			 pin_name(pin));
> diff --git a/drivers/acpi/pci_link.c b/drivers/acpi/pci_link.c
> index fb4c5632a232..219a644d739a 100644
> --- a/drivers/acpi/pci_link.c
> +++ b/drivers/acpi/pci_link.c
> @@ -59,6 +59,7 @@ struct acpi_pci_link_irq {
>  	u8 resource_type;
>  	u8 possible_count;
>  	u32 possible[ACPI_PCI_LINK_MAX_POSSIBLE];
> +	struct acpi_resource_source resource_source;
>  	u8 initialized:1;
>  	u8 reserved:7;
>  };
> @@ -120,6 +121,8 @@ static acpi_status acpi_pci_link_check_possible(struct acpi_resource *resource,
>  		{
>  			struct acpi_resource_extended_irq *p =
>  			    &resource->data.extended_irq;
> +			struct acpi_resource_source *rs =
> +			    &link->irq.resource_source;
>  			if (!p || !p->interrupt_count) {
>  				printk(KERN_WARNING PREFIX
>  					      "Blank _PRS EXT IRQ resource\n");
> @@ -140,6 +143,12 @@ static acpi_status acpi_pci_link_check_possible(struct acpi_resource *resource,
>  			link->irq.triggering = p->triggering;
>  			link->irq.polarity = p->polarity;
>  			link->irq.resource_type = ACPI_RESOURCE_TYPE_EXTENDED_IRQ;
> +			if (p->resource_source.string_length) {
> +				rs->index = p->resource_source.index;
> +				rs->string_length = p->resource_source.string_length;
> +				rs->string_ptr = kmalloc(rs->string_length, GFP_KERNEL);
> +				strcpy(rs->string_ptr, p->resource_source.string_ptr);
> +			}
>  			break;
>  		}
>  	default:
> @@ -326,7 +335,8 @@ static int acpi_pci_link_set(struct acpi_pci_link *link, int irq)
>  			resource->res.data.extended_irq.shareable = ACPI_SHARED;
>  		resource->res.data.extended_irq.interrupt_count = 1;
>  		resource->res.data.extended_irq.interrupts[0] = irq;
> -		/* ignore resource_source, it's optional */
> +		resource->res.data.extended_irq.resource_source =
> +			link->irq.resource_source;
>  		break;
>  	default:
>  		printk(KERN_ERR PREFIX "Invalid Resource_type %d\n", link->irq.resource_type);
> @@ -612,7 +622,7 @@ static int acpi_pci_link_allocate(struct acpi_pci_link *link)
>   * failure: return -1
>   */
>  int acpi_pci_link_allocate_irq(acpi_handle handle, int index, int *triggering,
> -			       int *polarity, char **name)
> +			       int *polarity, char **name, struct fwnode_handle **irq_domain)
>  {
>  	int result;
>  	struct acpi_device *device;
> @@ -656,6 +666,9 @@ int acpi_pci_link_allocate_irq(acpi_handle handle, int index, int *triggering,
>  		*polarity = link->irq.polarity;
>  	if (name)
>  		*name = acpi_device_bid(link->device);
> +	if (irq_domain)
> +		*irq_domain = acpi_get_irq_source_fwhandle(&link->irq.resource_source);
> +
>  	ACPI_DEBUG_PRINT((ACPI_DB_INFO,
>  			  "Link %s is referenced\n",
>  			  acpi_device_bid(link->device)));
> diff --git a/include/acpi/acpi_drivers.h b/include/acpi/acpi_drivers.h
> index 5eb175933a5b..6ff1ea76d476 100644
> --- a/include/acpi/acpi_drivers.h
> +++ b/include/acpi/acpi_drivers.h
> @@ -68,7 +68,7 @@
>  
>  int acpi_irq_penalty_init(void);
>  int acpi_pci_link_allocate_irq(acpi_handle handle, int index, int *triggering,
> -			       int *polarity, char **name);
> +			       int *polarity, char **name, struct fwnode_handle **irq_domain);
>  int acpi_pci_link_free_irq(acpi_handle handle);
>  
>  /* ACPI PCI Device Binding (pci_bind.c) */
> diff --git a/include/linux/acpi.h b/include/linux/acpi.h
> index 39263c6b52e1..5f1d7d3192fb 100644
> --- a/include/linux/acpi.h
> +++ b/include/linux/acpi.h
> @@ -324,6 +324,8 @@ extern int sbf_port;
>  extern unsigned long acpi_realmode_flags;
>  
>  int acpi_register_gsi (struct device *dev, u32 gsi, int triggering, int polarity);
> +int acpi_register_irq(struct device *dev, u32 gsi, int trigger,
> +		      int polarity, struct fwnode_handle *domain_id);

It looks like this declaration should be in drivers/acpi/internal.h,
since it's only used inside drivers/acpi/.

>  int acpi_gsi_to_irq (u32 gsi, unsigned int *irq);
>  int acpi_isa_irq_to_gsi (unsigned isa_irq, u32 *gsi);
>  
> @@ -336,6 +338,8 @@ struct irq_domain *acpi_irq_create_hierarchy(unsigned int flags,
>  					     const struct irq_domain_ops *ops,
>  					     void *host_data);
>  
> +struct fwnode_handle *acpi_get_irq_source_fwhandle(const struct acpi_resource_source *source);
> +
>  #ifdef CONFIG_X86_IO_APIC
>  extern int acpi_get_override_irq(u32 gsi, int *trigger, int *polarity);
>  #else
> -- 
> 2.28.0
>