[PATCH v2 2/2] platform-msi: Add ABI to show msi_irqs of platform devices

[Barry Song]

From: Barry Song <song.bao.hua@xxxxxxxxxxxxx>

Just like pci devices have msi_irqs which can be used by userspace irq affinity
tools or applications to bind irqs, platform devices also widely support msi
irqs. For platform devices, for example ARM SMMU, userspaces also care about
its msi irqs as applications can know the mapping between devices and irqs
and then make smarter decision on handling irq affinity. For example, for
SVA mode, it is better to pin io page fault to the numa node applications
are running on. Otherwise, io page fault will get a remote page from the
node iopf happens.
With this patch, a system with multiple arm SMMUs in multiple different numa
node can get the mapping between devices and irqs now:
root@ubuntu:/sys/devices/platform# ls -l arm-smmu-v3.*/msi_irqs/*
-r--r--r-- 1 root root 4096 Aug 11 10:29 arm-smmu-v3.0.auto/msi_irqs/25
-r--r--r-- 1 root root 4096 Aug 11 10:29 arm-smmu-v3.0.auto/msi_irqs/26
-r--r--r-- 1 root root 4096 Aug 11 10:28 arm-smmu-v3.1.auto/msi_irqs/27
-r--r--r-- 1 root root 4096 Aug 11 10:28 arm-smmu-v3.1.auto/msi_irqs/28
-r--r--r-- 1 root root 4096 Aug 11 10:29 arm-smmu-v3.2.auto/msi_irqs/29
-r--r--r-- 1 root root 4096 Aug 11 10:29 arm-smmu-v3.2.auto/msi_irqs/30
-r--r--r-- 1 root root 4096 Aug 11 10:29 arm-smmu-v3.3.auto/msi_irqs/31
-r--r--r-- 1 root root 4096 Aug 11 10:29 arm-smmu-v3.3.auto/msi_irqs/32
-r--r--r-- 1 root root 4096 Aug 11 10:29 arm-smmu-v3.4.auto/msi_irqs/33
-r--r--r-- 1 root root 4096 Aug 11 10:29 arm-smmu-v3.4.auto/msi_irqs/34
-r--r--r-- 1 root root 4096 Aug 11 10:29 arm-smmu-v3.5.auto/msi_irqs/35
-r--r--r-- 1 root root 4096 Aug 11 10:29 arm-smmu-v3.5.auto/msi_irqs/36
-r--r--r-- 1 root root 4096 Aug 11 10:29 arm-smmu-v3.6.auto/msi_irqs/37
-r--r--r-- 1 root root 4096 Aug 11 10:29 arm-smmu-v3.6.auto/msi_irqs/38
-r--r--r-- 1 root root 4096 Aug 11 10:29 arm-smmu-v3.7.auto/msi_irqs/39
-r--r--r-- 1 root root 4096 Aug 11 10:29 arm-smmu-v3.7.auto/msi_irqs/40

Applications can use the mapping and the numa node information to pin
irqs by leveraging the numa information which has also been exported:
root@ubuntu:/sys/devices/platform# cat arm-smmu-v3.0.auto/numa_node
0
root@ubuntu:/sys/devices/platform# cat arm-smmu-v3.4.auto/numa_node
2

Cc: Zhou Wang <wangzhou1@xxxxxxxxxxxxx>
Signed-off-by: Barry Song <song.bao.hua@xxxxxxxxxxxxx>
---
 Documentation/ABI/testing/sysfs-bus-platform | 14 ++++++++++++++
 drivers/base/platform-msi.c                  | 10 ++++++++++
 2 files changed, 24 insertions(+)

diff --git a/Documentation/ABI/testing/sysfs-bus-platform b/Documentation/ABI/testing/sysfs-bus-platform
index 194ca70..ff30728 100644
--- a/Documentation/ABI/testing/sysfs-bus-platform
+++ b/Documentation/ABI/testing/sysfs-bus-platform
@@ -28,3 +28,17 @@ Description:
 		value comes from an ACPI _PXM method or a similar firmware
 		source. Initial users for this file would be devices like
 		arm smmu which are populated by arm64 acpi_iort.
+
+What:		/sys/bus/platform/devices/.../msi_irqs/
+Date:		August 2021
+Contact:	Barry Song <song.bao.hua@xxxxxxxxxxxxx>
+Description:
+		The /sys/devices/.../msi_irqs directory contains a variable set
+		of files, with each file being named after a corresponding msi
+		irq vector allocated to that device.
+
+What:		/sys/bus/platform/devices/.../msi_irqs/<N>
+Date:		August 2021
+Contact:	Barry Song <song.bao.hua@xxxxxxxxxxxxx>
+Description:
+		This attribute will show "msi" if <N> is a valid msi irq
diff --git a/drivers/base/platform-msi.c b/drivers/base/platform-msi.c
index 0b72b13..a3bf910 100644
--- a/drivers/base/platform-msi.c
+++ b/drivers/base/platform-msi.c
@@ -23,6 +23,7 @@
 struct platform_msi_priv_data {
 	struct device		*dev;
 	void 			*host_data;
+	const struct attribute_group    **msi_irq_groups;
 	msi_alloc_info_t	arg;
 	irq_write_msi_msg_t	write_msg;
 	int			devid;
@@ -272,8 +273,16 @@ int platform_msi_domain_alloc_irqs(struct device *dev, unsigned int nvec,
 	if (err)
 		goto out_free_desc;
 
+	priv_data->msi_irq_groups = msi_populate_sysfs(dev);
+	if (IS_ERR(priv_data->msi_irq_groups)) {
+		err = PTR_ERR(priv_data->msi_irq_groups);
+		goto out_free_irqs;
+	}
+
 	return 0;
 
+out_free_irqs:
+	msi_domain_free_irqs(dev->msi_domain, dev);
 out_free_desc:
 	platform_msi_free_descs(dev, 0, nvec);
 out_free_priv_data:
@@ -293,6 +302,7 @@ void platform_msi_domain_free_irqs(struct device *dev)
 		struct msi_desc *desc;
 
 		desc = first_msi_entry(dev);
+		msi_destroy_sysfs(dev, desc->platform.msi_priv_data->msi_irq_groups);
 		platform_msi_free_priv_data(desc->platform.msi_priv_data);
 	}
 
-- 
1.8.3.1