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

Bjorn Helgaas
2021-05-11T19:22:06Z

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
>