Re: [PATCH] driver core: platform: expose numa_node to users in sysfs

[Greg KH]

On Tue, Jun 02, 2020 at 03:01:39PM +1200, Barry Song wrote:
> For some platform devices like iommu, particually ARM smmu, users may
> care about the numa locality. for example, if threads and drivers run
> near iommu, they may get much better performance on dma_unmap_sg.
> For other platform devices, users may still want to know the hardware
> topology.
> 
> Cc: Prime Zeng <prime.zeng@xxxxxxxxxxxxx>
> Cc: Robin Murphy <robin.murphy@xxxxxxx>
> Signed-off-by: Barry Song <song.bao.hua@xxxxxxxxxxxxx>
> ---
>  drivers/base/platform.c | 26 +++++++++++++++++++++++++-
>  1 file changed, 25 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/base/platform.c b/drivers/base/platform.c
> index b27d0f6c18c9..7794b9a38d82 100644
> --- a/drivers/base/platform.c
> +++ b/drivers/base/platform.c
> @@ -1062,13 +1062,37 @@ static ssize_t driver_override_show(struct device *dev,
>  }
>  static DEVICE_ATTR_RW(driver_override);
>  
> +static ssize_t numa_node_show(struct device *dev,
> +		struct device_attribute *attr, char *buf)
> +{
> +	return sprintf(buf, "%d\n", dev_to_node(dev));
> +}
> +static DEVICE_ATTR_RO(numa_node);
> +
> +static umode_t platform_dev_attrs_visible(struct kobject *kobj, struct attribute *a,
> +		int n)
> +{
> +	struct device *dev = container_of(kobj, typeof(*dev), kobj);
> +
> +	if (a == &dev_attr_numa_node.attr &&
> +			dev_to_node(dev) == NUMA_NO_NODE)
> +		return 0;
> +
> +	return a->mode;
> +}
>  
>  static struct attribute *platform_dev_attrs[] = {
>  	&dev_attr_modalias.attr,
> +	&dev_attr_numa_node.attr,
>  	&dev_attr_driver_override.attr,
>  	NULL,
>  };
> -ATTRIBUTE_GROUPS(platform_dev);
> +
> +static struct attribute_group platform_dev_group = {
> +	.attrs = platform_dev_attrs,
> +	.is_visible = platform_dev_attrs_visible,
> +};
> +__ATTRIBUTE_GROUPS(platform_dev);
>  
>  static int platform_uevent(struct device *dev, struct kobj_uevent_env *env)
>  {

Platform devices are NUMA?  That's crazy, and feels like a total abuse
of platform devices and drivers that really should belong on a "real"
bus.

What drivers in the kernel today have this issue?

thanks,

greg k-h