[RFC KERNEL PATCH v5 3/3] PCI/sysfs: Add gsi sysfs for pci_dev

[Jiqian Chen <Jiqian.Chen@amd.com>]

There is a need for some scenarios to use gsi sysfs.
For example, when xen passthrough a device to dumU, it will
use gsi to map pirq, but currently userspace can't get gsi
number.
So, add gsi sysfs for that and for other potential scenarios.

Co-developed-by: Huang Rui <ray.huang@amd.com>
Signed-off-by: Jiqian Chen <Jiqian.Chen@amd.com>
---
RFC: No feasible suggestions were obtained in the discussion of v4.
Discussions are still needed where/how to expose the gsi.
Looking forward to get more comments and suggestions from PCI/ACPI Maintainers.

---
 drivers/acpi/pci_irq.c  |  1 +
 drivers/pci/pci-sysfs.c | 11 +++++++++++
 include/linux/pci.h     |  2 ++
 3 files changed, 14 insertions(+)

diff --git a/drivers/acpi/pci_irq.c b/drivers/acpi/pci_irq.c
index 630fe0a34bc6..739a58755df2 100644
--- a/drivers/acpi/pci_irq.c
+++ b/drivers/acpi/pci_irq.c
@@ -449,6 +449,7 @@ int acpi_pci_irq_enable(struct pci_dev *dev)
 		kfree(entry);
 		return 0;
 	}
+	dev->gsi = gsi;
 
 	rc = acpi_register_gsi(&dev->dev, gsi, triggering, polarity);
 	if (rc < 0) {
diff --git a/drivers/pci/pci-sysfs.c b/drivers/pci/pci-sysfs.c
index 2321fdfefd7d..c51df88d079e 100644
--- a/drivers/pci/pci-sysfs.c
+++ b/drivers/pci/pci-sysfs.c
@@ -71,6 +71,16 @@ static ssize_t irq_show(struct device *dev,
 }
 static DEVICE_ATTR_RO(irq);
 
+static ssize_t gsi_show(struct device *dev,
+			struct device_attribute *attr,
+			char *buf)
+{
+	struct pci_dev *pdev = to_pci_dev(dev);
+
+	return sysfs_emit(buf, "%u\n", pdev->gsi);
+}
+static DEVICE_ATTR_RO(gsi);
+
 static ssize_t broken_parity_status_show(struct device *dev,
 					 struct device_attribute *attr,
 					 char *buf)
@@ -596,6 +606,7 @@ static struct attribute *pci_dev_attrs[] = {
 	&dev_attr_revision.attr,
 	&dev_attr_class.attr,
 	&dev_attr_irq.attr,
+	&dev_attr_gsi.attr,
 	&dev_attr_local_cpus.attr,
 	&dev_attr_local_cpulist.attr,
 	&dev_attr_modalias.attr,
diff --git a/include/linux/pci.h b/include/linux/pci.h
index 7ab0d13672da..457043cfdfce 100644
--- a/include/linux/pci.h
+++ b/include/linux/pci.h
@@ -529,6 +529,8 @@ struct pci_dev {
 
 	/* These methods index pci_reset_fn_methods[] */
 	u8 reset_methods[PCI_NUM_RESET_METHODS]; /* In priority order */
+
+	unsigned int	gsi;
 };
 
 static inline struct pci_dev *pci_physfn(struct pci_dev *dev)
-- 
2.34.1