Re: [PATCH] platform-msi: Add ABI to show msi_irqs of platform devices

[Greg KH <gregkh@linuxfoundation.org>]

On Wed, Aug 11, 2021 at 10:50:20PM +1200, Barry Song wrote:
> 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@hisilicon.com>
> Signed-off-by: Barry Song <song.bao.hua@hisilicon.com>
> ---
>  Documentation/ABI/testing/sysfs-bus-platform |  14 +++
>  drivers/base/platform-msi.c                  | 122 +++++++++++++++++++++++++++
>  2 files changed, 136 insertions(+)
> 
> diff --git a/Documentation/ABI/testing/sysfs-bus-platform b/Documentation/ABI/testing/sysfs-bus-platform
> index 194ca70..4498f89 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@hisilicon.com>
> +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@hisilicon.com>
> +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..6a72ebc 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;
> @@ -245,6 +246,120 @@ static void platform_msi_free_priv_data(struct platform_msi_priv_data *data)
>  	kfree(data);
>  }
>  
> +static ssize_t platform_msi_show(struct device *dev, struct device_attribute *attr,
> +			     char *buf)
> +{
> +	struct msi_desc *entry;
> +	unsigned long irq;
> +	int retval;
> +
> +	retval = kstrtoul(attr->attr.name, 10, &irq);
> +	if (retval)
> +		return retval;
> +
> +	entry = irq_get_msi_desc(irq);
> +	if (entry)
> +		return sprintf(buf, "msi\n");

sysfs_emit()?

But why isn't this all handled by the MSI core code?  Why would each bus
need to have this logic in it?

thanks,

greg k-h