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From:   Rajat Jain <rajatja@google.com>
Date:   Mon, 24 May 2021 10:25:06 -0700
Message-ID: <CACK8Z6EsX27pyakKbdH-tjV+=m1QZ+KzFD-A-BNXX-tkOjtt9g@mail.gmail.com>
Subject: Re: [PATCH v4 1/2] driver core: Move the "removable" attribute from
 USB to core
To:     Bjorn Helgaas <helgaas@kernel.org>
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        "Rafael J. Wysocki" <rafael@kernel.org>,
        Bjorn Helgaas <bhelgaas@google.com>,
        Alan Stern <stern@rowland.harvard.edu>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        linux-pci <linux-pci@vger.kernel.org>,
        "open list:ULTRA-WIDEBAND (UWB) SUBSYSTEM:" 
        <linux-usb@vger.kernel.org>, Oliver Neukum <oneukum@suse.com>,
        David Laight <David.Laight@aculab.com>,
        =?UTF-8?Q?Krzysztof_Wilczy=C5=84ski?= <kw@linux.com>,
        Rajat Jain <rajatxjain@gmail.com>,
        Jesse Barnes <jsbarnes@google.com>,
        Dmitry Torokhov <dtor@google.com>
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

On Fri, May 21, 2021 at 1:54 PM Bjorn Helgaas <helgaas@kernel.org> 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@google.com>
>
> Reviewed-by: Bjorn Helgaas <bhelgaas@google.com>
>
> 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@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..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@gmail.com>
> > +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
> >