Re: [PATCH v4 1/2] driver core: Move the "removable" attribute from USB to core

From: Rajat Jain
Date: Mon May 24 2021 - 13:25:47 EST

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On Fri, May 21, 2021 at 1:54 PM Bjorn Helgaas <helgaas@xxxxxxxxxx> wrote:
>
> On Thu, May 13, 2021 at 04:27:00PM -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 populate the removable property of the device while
> > enumerating it with the 3 possible values -
> > - "unknown"
> > - "fixed"
> > - "removable"
> > Leaving the field unchanged (i.e. "not supported") would mean that the
> > attribute would not show up in sysfs for that device. The UAPI (location,
> > symantics etc) for the attribute remains unchanged.
>
> Looks nice!
>
> Maybe the mini usage guide here could be a little more explicit, e.g.,
>
> Move the "removable" attribute from USB to the device core so it can
> be used by other subsystems / buses.
>
> By default, devices do not have a "removable" attribute in sysfs.
>
> If a subsystem or bus driver wants to support a "removable"
> attribute, it should call device_set_removable() before calling
> device_register() or device_add(), e.g.,
>
> device_set_removable(dev, DEVICE_REMOVABLE);
> device_register(dev);
>
> The possible values and the resulting sysfs attribute contents are:
>
> DEVICE_REMOVABLE_UNKNOWN -> "unknown"
> DEVICE_REMOVABLE -> "removable"
> DEVICE_FIXED -> "fixed"
>
> Convert the USB "removable" attribute to use this new device core
> functionality. There should be no user-visible change in the
> location or semantics of attribute for USB devices.
>
> > Signed-off-by: Rajat Jain <rajatja@xxxxxxxxxx>
>
> Reviewed-by: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>
>
> Minor comment below, reviewed-by applies whether or not you do
> anything.

Thanks Bjorn for your review, I took care of both the comments and
updated the commit log.

>
> > ---
> > v4: - instead of devicce_type->supports_removable, add 1 more value in
> > device_removable_enum
> > - documentation update.
> > - Remove "Acked-by" and "Reviewed-by" tags from previous versions.
> > v3: - Minor commit log / comments updated.
> > - use sysfs_emit()
> > - Rename local variable name (state -> loc)
> > - change supports_removable flag from bool to bitfield.
> > 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 | 13 ++++---
> > drivers/usb/core/sysfs.c | 24 ------------
> > include/linux/device.h | 37 +++++++++++++++++++
> > include/linux/usb.h | 7 ----
> > 7 files changed, 89 insertions(+), 48 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@xxxxxxxxxx>
> > -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@xxxxxxxxxxxxxxx>
> > diff --git a/Documentation/ABI/testing/sysfs-devices-removable b/Documentation/ABI/testing/sysfs-devices-removable
> > new file mode 100644
> > index 000000000000..acf7766e800b
> > --- /dev/null
> > +++ b/Documentation/ABI/testing/sysfs-devices-removable
> > @@ -0,0 +1,17 @@
> > +What: /sys/devices/.../removable
> > +Date: May 2021
> > +Contact: Rajat Jain <rajatxjain@xxxxxxxxx>
> > +Description:
> > + Information about whether a given device can be removed from the
> > + platform by the user. This is determined by its subsystem in a
> > + bus / platform-specific way. This attribute is only present for
> > + devices that can support determining such information:
> > +
> > + "removable": device can be removed from the platform by the user
> > + "fixed": device is fixed to the platform / cannot be removed
> > + by the user.
> > + "unknown": The information is unavailable / cannot be deduced.
> > +
> > + 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 4a8bf8cda52b..ae3d6a4a79fb 100644
> > --- a/drivers/base/core.c
> > +++ b/drivers/base/core.c
> > @@ -2404,6 +2404,25 @@ 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 *loc;
> > +
> > + switch (dev->removable) {
> > + case DEVICE_REMOVABLE:
> > + loc = "removable";
> > + break;
> > + case DEVICE_FIXED:
> > + loc = "fixed";
> > + break;
> > + default:
> > + loc = "unknown";
> > + }
> > + return sysfs_emit(buf, "%s\n", loc);
> > +}
> > +static DEVICE_ATTR_RO(removable);
> > +
> > int device_add_groups(struct device *dev, const struct attribute_group **groups)
> > {
> > return sysfs_create_groups(&dev->kobj, groups);
> > @@ -2581,8 +2600,16 @@ static int device_add_attrs(struct device *dev)
> > goto err_remove_dev_online;
> > }
> >
> > + if (dev_removable_is_valid(dev)) {
> > + 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:
> > @@ -2602,6 +2629,7 @@ 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 b2bc4b7c4289..366cb7ef3b72 100644
> > --- a/drivers/usb/core/hub.c
> > +++ b/drivers/usb/core/hub.c
> > @@ -2432,6 +2432,8 @@ static void set_usb_port_removable(struct usb_device *udev)
> > u16 wHubCharacteristics;
> > bool removable = true;
> >
> > + dev_set_removable(&udev->dev, DEVICE_REMOVABLE_UNKNOWN);
> > +
> > if (!hdev)
> > return;
> >
> > @@ -2443,11 +2445,11 @@ 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;
> > @@ -2472,9 +2474,9 @@ 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);
> >
> > }
> >
> > @@ -2546,8 +2548,7 @@ int usb_new_device(struct usb_device *udev)
> > device_enable_async_suspend(&udev->dev);
> >
> > /* check whether the hub or firmware marks this port as non-removable */
> > - if (udev->parent)
> > - set_usb_port_removable(udev);
> > + set_usb_port_removable(udev);
> >
> > /* Register the device. The device driver is responsible
> > * for configuring the device and invoking the add-device
> > diff --git a/drivers/usb/core/sysfs.c b/drivers/usb/core/sysfs.c
> > index 5a168ba9fc51..fa2e49d432ff 100644
> > --- a/drivers/usb/core/sysfs.c
> > +++ b/drivers/usb/core/sysfs.c
> > @@ -301,29 +301,6 @@ 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)
> > {
> > @@ -828,7 +805,6 @@ 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/include/linux/device.h b/include/linux/device.h
> > index 38a2071cf776..e3a4749694b7 100644
> > --- a/include/linux/device.h
> > +++ b/include/linux/device.h
> > @@ -350,6 +350,22 @@ 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.
> > + * @DEVICE_REMOVABLE_NOT_SUPPORTED: This attribute is not supported for this
> > + * device (default).
> > + * @DEVICE_REMOVABLE_UNKNOWN: Device location is Unknown.
> > + * @DEVICE_FIXED: Device is not removable by the user.
> > + * @DEVICE_REMOVABLE: Device is removable by the user.
> > + */
> > +enum device_removable {
> > + DEVICE_REMOVABLE_NOT_SUPPORTED = 0, /* must be 0 */
> > + DEVICE_REMOVABLE_UNKNOWN,
> > + DEVICE_FIXED,
> > + DEVICE_REMOVABLE,
> > +};
> > +
> > /**
> > * struct dev_links_info - Device data related to device links.
> > * @suppliers: List of links to supplier devices.
> > @@ -431,6 +447,9 @@ 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().
> > @@ -544,6 +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;
> > @@ -782,6 +803,22 @@ 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->removable == DEVICE_REMOVABLE;
> > +}
> > +
> > +static inline bool dev_removable_is_valid(struct device *dev)
> > +{
> > + return dev && dev->removable != DEVICE_REMOVABLE_NOT_SUPPORTED;
>
> I probably wouldn't check for "dev" being non-NULL in these two
> functions unless you have a use case that requires it.

Done, I removed the check and submitted the v5 here:
https://lore.kernel.org/patchwork/patch/1435682/

Thanks,

Rajat

>
> > +}
> > +
> > /*
> > * High level routines for use by the bus drivers
> > */
> > diff --git a/include/linux/usb.h b/include/linux/usb.h
> > index eaae24217e8a..b9bd664f44a1 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,
> > @@ -703,7 +697,6 @@ 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;
> > --
> > 2.31.1.751.gd2f1c929bd-goog
> >

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