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

[Rajat Jain]

Hi Bjorn,

Thanks for the review.

On Tue, May 11, 2021 at 12:22 PM Bjorn Helgaas <helgaas@xxxxxxxxxx> wrote:
>
> 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.


Yes, that is correct.

>
>
> Wrap above to fill 75 columns.


Will do.

>
>
> > Signed-off-by: Rajat Jain <rajatja@xxxxxxxxxx>
>
> Looks reasonable to me.  Trivial comments below.
>
> Reviewed-by: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>
>
> > ---
> > 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@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..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@xxxxxxxxxx>,
> > +             Rajat Jain <rajatja@xxxxxxxxxx>
> > +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/

Will do.

>
> > +             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

Will do.

>
> 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;

Will do.

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

Will do.

>
> >  };
> >
> >  /* 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/

Will do.

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

I'd prefer to keep the comment because I feel it makes it clear that
different buses may employ different criteria to decide what
classifies as "removable" vs "fixed".

Thanks,

Rajat



>
> > + * @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
> >