Re: [PATCH v2 1/2] driver core: Move the "removable" attribute from USB to core

[Bjorn Helgaas <helgaas@kernel.org>]

On Fri, Apr 23, 2021 at 07:16:30PM -0700, Rajat Jain wrote:
> Move the "removable" attribute from USB to core in order to allow
> it to be supported by other subsystem / buses. Individual buses
> that want to support this attribute can opt-in by setting the
> supports_removable flag, and then populating the removable property
> of the device while enumerating it. The ABI for the attribute remains
> unchanged.

Thanks for confirming that the sysfs ABI is unchanged -- it wasn't
obvious to me from the doc descriptions below that the "removable"
file appears in the exact same place it did before.

Wrap above to fill 75 columns.

> Signed-off-by: Rajat Jain <rajatja@google.com>

Looks reasonable to me.  Trivial comments below.

Reviewed-by: Bjorn Helgaas <bhelgaas@google.com>

> ---
> v2: Add documentation
> 
>  Documentation/ABI/testing/sysfs-bus-usb       | 11 ------
>  .../ABI/testing/sysfs-devices-removable       | 17 +++++++++
>  drivers/base/core.c                           | 28 +++++++++++++++
>  drivers/usb/core/hub.c                        |  8 ++---
>  drivers/usb/core/sysfs.c                      | 24 -------------
>  drivers/usb/core/usb.c                        |  1 +
>  include/linux/device.h                        | 36 +++++++++++++++++++
>  include/linux/usb.h                           |  7 ----
>  8 files changed, 86 insertions(+), 46 deletions(-)
>  create mode 100644 Documentation/ABI/testing/sysfs-devices-removable
> 
> diff --git a/Documentation/ABI/testing/sysfs-bus-usb b/Documentation/ABI/testing/sysfs-bus-usb
> index bf2c1968525f..73eb23bc1f34 100644
> --- a/Documentation/ABI/testing/sysfs-bus-usb
> +++ b/Documentation/ABI/testing/sysfs-bus-usb
> @@ -154,17 +154,6 @@ Description:
>  		files hold a string value (enable or disable) indicating whether
>  		or not USB3 hardware LPM U1 or U2 is enabled for the device.
>  
> -What:		/sys/bus/usb/devices/.../removable
> -Date:		February 2012
> -Contact:	Matthew Garrett <mjg@redhat.com>
> -Description:
> -		Some information about whether a given USB device is
> -		physically fixed to the platform can be inferred from a
> -		combination of hub descriptor bits and platform-specific data
> -		such as ACPI. This file will read either "removable" or
> -		"fixed" if the information is available, and "unknown"
> -		otherwise.
> -
>  What:		/sys/bus/usb/devices/.../ltm_capable
>  Date:		July 2012
>  Contact:	Sarah Sharp <sarah.a.sharp@linux.intel.com>
> diff --git a/Documentation/ABI/testing/sysfs-devices-removable b/Documentation/ABI/testing/sysfs-devices-removable
> new file mode 100644
> index 000000000000..e13dddd547b5
> --- /dev/null
> +++ b/Documentation/ABI/testing/sysfs-devices-removable
> @@ -0,0 +1,17 @@
> +What:		/sys/devices/.../removable
> +Date:		Apr 2021
> +Contact:	Matthew Garrett <mjg@redhat.com>,
> +		Rajat Jain <rajatja@google.com>
> +Description:
> +		Information about whether a given device is physically fixed to
> +		the platform. This is determined by the device's subsystem in a
> +		bus / platform specific way. This attribute is only present for

s/platform specific/platform-specific/

> +		buses that can support determining such information:
> +
> +		"removable": The device is external / removable from the system.
> +		"fixed":     The device is internal / fixed to the system.
> +		"unknown":   The information is unavailable.
> +
> +		Currently this is only supported by USB (which infers the
> +		information from a combination of hub descriptor bits and
> +		platform-specific data such as ACPI).
> diff --git a/drivers/base/core.c b/drivers/base/core.c
> index f29839382f81..b8ae4cc52805 100644
> --- a/drivers/base/core.c
> +++ b/drivers/base/core.c
> @@ -2327,6 +2327,25 @@ static ssize_t online_store(struct device *dev, struct device_attribute *attr,
>  }
>  static DEVICE_ATTR_RW(online);
>  
> +static ssize_t removable_show(struct device *dev, struct device_attribute *attr,
> +			      char *buf)
> +{
> +	const char *state;
> +
> +	switch (dev->removable) {
> +	case DEVICE_REMOVABLE:
> +		state = "removable";
> +		break;
> +	case DEVICE_FIXED:
> +		state = "fixed";
> +		break;
> +	default:
> +		state = "unknown";
> +	}
> +	return sprintf(buf, "%s\n", state);

Maybe sysfs_emit()?

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/filesystems/sysfs.rst?id=v5.12#n246

Ironically, the example below the admonition to use sysfs_emit() still
uses scnprintf() :)

> +}
> +static DEVICE_ATTR_RO(removable);
> +
>  int device_add_groups(struct device *dev, const struct attribute_group **groups)
>  {
>  	return sysfs_create_groups(&dev->kobj, groups);
> @@ -2504,8 +2523,16 @@ static int device_add_attrs(struct device *dev)
>  			goto err_remove_dev_online;
>  	}
>  
> +	if (type && type->supports_removable) {
> +		error = device_create_file(dev, &dev_attr_removable);
> +		if (error)
> +			goto err_remove_dev_waiting_for_supplier;
> +	}
> +
>  	return 0;
>  
> + err_remove_dev_waiting_for_supplier:
> +	device_remove_file(dev, &dev_attr_waiting_for_supplier);
>   err_remove_dev_online:
>  	device_remove_file(dev, &dev_attr_online);
>   err_remove_dev_groups:
> @@ -2525,6 +2552,7 @@ static void device_remove_attrs(struct device *dev)
>  	struct class *class = dev->class;
>  	const struct device_type *type = dev->type;
>  
> +	device_remove_file(dev, &dev_attr_removable);
>  	device_remove_file(dev, &dev_attr_waiting_for_supplier);
>  	device_remove_file(dev, &dev_attr_online);
>  	device_remove_groups(dev, dev->groups);
> diff --git a/drivers/usb/core/hub.c b/drivers/usb/core/hub.c
> index 7f71218cc1e5..500e5648de04 100644
> --- a/drivers/usb/core/hub.c
> +++ b/drivers/usb/core/hub.c
> @@ -2442,11 +2442,11 @@ static void set_usb_port_removable(struct usb_device *udev)
>  	 */
>  	switch (hub->ports[udev->portnum - 1]->connect_type) {
>  	case USB_PORT_CONNECT_TYPE_HOT_PLUG:
> -		udev->removable = USB_DEVICE_REMOVABLE;
> +		dev_set_removable(&udev->dev, DEVICE_REMOVABLE);
>  		return;
>  	case USB_PORT_CONNECT_TYPE_HARD_WIRED:
>  	case USB_PORT_NOT_USED:
> -		udev->removable = USB_DEVICE_FIXED;
> +		dev_set_removable(&udev->dev, DEVICE_FIXED);
>  		return;
>  	default:
>  		break;
> @@ -2471,9 +2471,9 @@ static void set_usb_port_removable(struct usb_device *udev)
>  	}
>  
>  	if (removable)
> -		udev->removable = USB_DEVICE_REMOVABLE;
> +		dev_set_removable(&udev->dev, DEVICE_REMOVABLE);
>  	else
> -		udev->removable = USB_DEVICE_FIXED;
> +		dev_set_removable(&udev->dev, DEVICE_FIXED);
>  
>  }
>  
> diff --git a/drivers/usb/core/sysfs.c b/drivers/usb/core/sysfs.c
> index d85699bee671..e8ff3afdf7af 100644
> --- a/drivers/usb/core/sysfs.c
> +++ b/drivers/usb/core/sysfs.c
> @@ -298,29 +298,6 @@ static ssize_t urbnum_show(struct device *dev, struct device_attribute *attr,
>  }
>  static DEVICE_ATTR_RO(urbnum);
>  
> -static ssize_t removable_show(struct device *dev, struct device_attribute *attr,
> -			      char *buf)
> -{
> -	struct usb_device *udev;
> -	char *state;
> -
> -	udev = to_usb_device(dev);
> -
> -	switch (udev->removable) {
> -	case USB_DEVICE_REMOVABLE:
> -		state = "removable";
> -		break;
> -	case USB_DEVICE_FIXED:
> -		state = "fixed";
> -		break;
> -	default:
> -		state = "unknown";
> -	}
> -
> -	return sprintf(buf, "%s\n", state);
> -}
> -static DEVICE_ATTR_RO(removable);
> -
>  static ssize_t ltm_capable_show(struct device *dev,
>  				struct device_attribute *attr, char *buf)
>  {
> @@ -825,7 +802,6 @@ static struct attribute *dev_attrs[] = {
>  	&dev_attr_avoid_reset_quirk.attr,
>  	&dev_attr_authorized.attr,
>  	&dev_attr_remove.attr,
> -	&dev_attr_removable.attr,
>  	&dev_attr_ltm_capable.attr,
>  #ifdef CONFIG_OF
>  	&dev_attr_devspec.attr,
> diff --git a/drivers/usb/core/usb.c b/drivers/usb/core/usb.c
> index a566bb494e24..5a0f73a28196 100644
> --- a/drivers/usb/core/usb.c
> +++ b/drivers/usb/core/usb.c
> @@ -523,6 +523,7 @@ struct device_type usb_device_type = {
>  #ifdef CONFIG_PM
>  	.pm =		&usb_device_pm_ops,
>  #endif
> +	.supports_removable = true,
>  };
>  
>  
> diff --git a/include/linux/device.h b/include/linux/device.h
> index ba660731bd25..d6442b811607 100644
> --- a/include/linux/device.h
> +++ b/include/linux/device.h
> @@ -93,6 +93,12 @@ struct device_type {
>  	void (*release)(struct device *dev);
>  
>  	const struct dev_pm_ops *pm;
> +
> +	/*
> +	 * Determines whether the subsystem supports classifying the devices of
> +	 * this type into removable vs fixed.
> +	 */

Doesn't really match comment style in rest of the file.  Seems pretty
self-explanatory, maybe doesn't even need a comment, or perhaps a
short comment like this:

	bool supports_removable:1;  /* subsystem supplies info */

> +	bool supports_removable;

Most boolean structure members in this file are bitfields, e.g.,
"bool offline:1".

>  };
>  
>  /* interface for exporting device attributes */
> @@ -350,6 +356,19 @@ enum dl_dev_state {
>  	DL_DEV_UNBINDING,
>  };
>  
> +/**
> + * enum device_removable - Whether the device is removable. The criteria for a
> + * device to be classified as removable, is determined by its subsystem or bus.

s/removable,/removable/

Or maybe drop the whole "The criteria ..." sentence?  Not sure it adds
much useful info.

> + * @DEVICE_REMOVABLE_UNKNOWN:  Device location is Unknown (default).
> + * @DEVICE_REMOVABLE: Device is removable by the user.
> + * @DEVICE_FIXED: Device is not removable by the user.
> + */
> +enum device_removable {
> +	DEVICE_REMOVABLE_UNKNOWN = 0,
> +	DEVICE_REMOVABLE,
> +	DEVICE_FIXED,
> +};
> +
>  /**
>   * struct dev_links_info - Device data related to device links.
>   * @suppliers: List of links to supplier devices.
> @@ -431,6 +450,9 @@ struct dev_links_info {
>   * 		device (i.e. the bus driver that discovered the device).
>   * @iommu_group: IOMMU group the device belongs to.
>   * @iommu:	Per device generic IOMMU runtime data
> + * @removable:  Whether the device can be removed from the system. This
> + *              should be set by the subsystem / bus driver that discovered
> + *              the device.
>   *
>   * @offline_disabled: If set, the device is permanently online.
>   * @offline:	Set after successful invocation of bus type's .offline().
> @@ -541,6 +563,8 @@ struct device {
>  	struct iommu_group	*iommu_group;
>  	struct dev_iommu	*iommu;
>  
> +	enum device_removable	removable;
> +
>  	bool			offline_disabled:1;
>  	bool			offline:1;
>  	bool			of_node_reused:1;
> @@ -778,6 +802,18 @@ static inline bool dev_has_sync_state(struct device *dev)
>  	return false;
>  }
>  
> +static inline void dev_set_removable(struct device *dev,
> +				     enum device_removable removable)
> +{
> +	dev->removable = removable;
> +}
> +
> +static inline bool dev_is_removable(struct device *dev)
> +{
> +	return dev && dev->type && dev->type->supports_removable
> +	    && dev->removable == DEVICE_REMOVABLE;
> +}
> +
>  /*
>   * High level routines for use by the bus drivers
>   */
> diff --git a/include/linux/usb.h b/include/linux/usb.h
> index d6a41841b93e..0bbb9e8b18c7 100644
> --- a/include/linux/usb.h
> +++ b/include/linux/usb.h
> @@ -473,12 +473,6 @@ struct usb_dev_state;
>  
>  struct usb_tt;
>  
> -enum usb_device_removable {
> -	USB_DEVICE_REMOVABLE_UNKNOWN = 0,
> -	USB_DEVICE_REMOVABLE,
> -	USB_DEVICE_FIXED,
> -};
> -
>  enum usb_port_connect_type {
>  	USB_PORT_CONNECT_TYPE_UNKNOWN = 0,
>  	USB_PORT_CONNECT_TYPE_HOT_PLUG,
> @@ -701,7 +695,6 @@ struct usb_device {
>  #endif
>  	struct wusb_dev *wusb_dev;
>  	int slot_id;
> -	enum usb_device_removable removable;
>  	struct usb2_lpm_parameters l1_params;
>  	struct usb3_lpm_parameters u1_params;
>  	struct usb3_lpm_parameters u2_params;
> -- 
> 2.31.1.498.g6c1eba8ee3d-goog
>