Re: [PATCH] usb: storage: Add ums-cros-aoa driver

[Matthew Dharm <mdharm-usb@one-eyed-alien.net>]

(Sending this again, because I forgot to switch my mail client to
plain-text-only last time).

Why not do the mode switch from userspace?  I thought we were trying
to move all the mode-switching stuff in that direction.....

Matt


On Tue, Aug 27, 2019 at 4:14 PM Julius Werner <jwerner@chromium.org> wrote:
>
> This patch adds a new "unusual" USB mass storage device driver. This
> driver will be used for a virtual USB storage device presented by an
> Android phone running the 'Chrome OS Recovery'* Android app. This app
> uses the Android Open Accessory (AOA) API to talk directly to a USB host
> attached to the phone.
>
> The AOA protocol requires the host to send a custom vendor command on
> EP0 to "switch" the phone into "AOA mode" (making it drop off the bus
> and reenumerate with different descriptors). The ums-cros-aoa driver is
> just a small stub driver to send these vendor commands. It identifies
> the device it should operate on by VID/PID passed in through a module
> parameter (e.g. from the bootloader). After the phone is in AOA mode,
> the normal USB mass storage stack will recognize it by its special
> VID/PID like any other "unusual dev". An initializer function will
> further double-check that the device is the device previously operated
> on by ums-cros-aoa.
>
> *NOTE: The Android app is still under development and will be released
> at a later date. I'm submitting this patch now so that the driver name
> and module parameters can be set in stone already, because I have to
> bake them into bootloader code that is not field-updatable.
>
> Signed-off-by: Julius Werner <jwerner@chromium.org>
> ---
>  drivers/usb/storage/Kconfig        |  12 +++
>  drivers/usb/storage/Makefile       |   2 +
>  drivers/usb/storage/cros-aoa.c     | 129 +++++++++++++++++++++++++++++
>  drivers/usb/storage/initializers.c |  34 ++++++++
>  drivers/usb/storage/initializers.h |   4 +
>  drivers/usb/storage/unusual_devs.h |  18 ++++
>  6 files changed, 199 insertions(+)
>  create mode 100644 drivers/usb/storage/cros-aoa.c
>
> diff --git a/drivers/usb/storage/Kconfig b/drivers/usb/storage/Kconfig
> index 59aad38b490a6..cc901ee2bb766 100644
> --- a/drivers/usb/storage/Kconfig
> +++ b/drivers/usb/storage/Kconfig
> @@ -184,6 +184,18 @@ config USB_STORAGE_ENE_UB6250
>           To compile this driver as a module, choose M here: the
>           module will be called ums-eneub6250.
>
> +config USB_STORAGE_CROS_AOA
> +       tristate "Support for connecting to Chrome OS Recovery Android app"
> +       default n
> +       depends on USB_STORAGE
> +       help
> +         Say Y here if you want to connect an Android phone running the Chrome
> +         OS Recovery app to this device and mount the image served by that app
> +         as a virtual storage device. Unless you're building for Chrome OS, you
> +         probably want to say N.
> +
> +         If this driver is compiled as a module, it will be named ums-cros-aoa.
> +
>  endif # USB_STORAGE
>
>  config USB_UAS
> diff --git a/drivers/usb/storage/Makefile b/drivers/usb/storage/Makefile
> index a67ddcbb4e249..f734741d4658b 100644
> --- a/drivers/usb/storage/Makefile
> +++ b/drivers/usb/storage/Makefile
> @@ -17,6 +17,7 @@ usb-storage-y += usual-tables.o
>  usb-storage-$(CONFIG_USB_STORAGE_DEBUG) += debug.o
>
>  obj-$(CONFIG_USB_STORAGE_ALAUDA)       += ums-alauda.o
> +obj-$(CONFIG_USB_STORAGE_CROS_AOA)     += ums-cros-aoa.o
>  obj-$(CONFIG_USB_STORAGE_CYPRESS_ATACB) += ums-cypress.o
>  obj-$(CONFIG_USB_STORAGE_DATAFAB)      += ums-datafab.o
>  obj-$(CONFIG_USB_STORAGE_ENE_UB6250)   += ums-eneub6250.o
> @@ -31,6 +32,7 @@ obj-$(CONFIG_USB_STORAGE_SDDR55)      += ums-sddr55.o
>  obj-$(CONFIG_USB_STORAGE_USBAT)                += ums-usbat.o
>
>  ums-alauda-y           := alauda.o
> +ums-cros-aoa-y         := cros-aoa.o
>  ums-cypress-y          := cypress_atacb.o
>  ums-datafab-y          := datafab.o
>  ums-eneub6250-y                := ene_ub6250.o
> diff --git a/drivers/usb/storage/cros-aoa.c b/drivers/usb/storage/cros-aoa.c
> new file mode 100644
> index 0000000000000..269e9193209d9
> --- /dev/null
> +++ b/drivers/usb/storage/cros-aoa.c
> @@ -0,0 +1,129 @@
> +// SPDX-License-Identifier: GPL-2 WITH Linux-syscall-note
> +/*
> + * Driver for Chrome OS Recovery via Android Open Accessory
> + *
> + * (c) 2019 Google LLC (Julius Werner <jwerner@chromium.org>)
> + *
> + * This driver connects to an Android device via the Android Open Accessory
> + * protocol to use it as a USB storage back-end. It is used for system recovery
> + * on Chrome OS. The descriptors sent are specific to the Chrome OS Recovery app
> + * for Android. The driver is inert unless activated by boot firmware with an
> + * explicit kernel command line parameter.
> + */
> +
> +#include <linux/module.h>
> +#include <linux/printk.h>
> +#include <linux/usb.h>
> +
> +#include "initializers.h"
> +
> +#define DRV_NAME "ums-cros-aoa"
> +
> +MODULE_DESCRIPTION("Driver for Chrome OS Recovery via Android Open Accessory");
> +MODULE_AUTHOR("Julius Werner <jwerner@chromium.org>");
> +MODULE_LICENSE("GPL");
> +
> +#define AOA_GET_PROTOCOL       51
> +#define AOA_SET_STRING         52
> +#define AOA_START              53
> +
> +#define AOA_STR_MANUFACTURER   0
> +#define AOA_STR_MODEL          1
> +#define AOA_STR_DESCRIPTION    2
> +#define AOA_STR_VERSION                3
> +#define AOA_STR_URI            4
> +#define AOA_STR_SERIAL         5
> +
> +#define CROS_MANUF             "Google"
> +#define CROS_MODEL             "Chrome OS Recovery"
> +#define CROS_DESC              "Chrome OS device in Recovery Mode"
> +#define CROS_VERSION           "1.0"
> +#define CROS_URI               "https://google.com/chromeos/recovery_android"
> +
> +static char *bind;
> +module_param(bind, charp, 0);
> +
> +static struct usb_device_id cros_aoa_ids[] = {
> +       { USB_DEVICE(0, 0) },   /* to be filled out by cros_aoa_init() */
> +       { }
> +};
> +/* No MODULE_DEVICE_TABLE(). Autoloading doesn't make sense for this module. */
> +
> +static int set_string(struct usb_device *udev, u16 type, const char *string)
> +{
> +       return usb_control_msg(udev, usb_sndctrlpipe(udev, 0), AOA_SET_STRING,
> +                              USB_DIR_OUT | USB_TYPE_VENDOR | USB_RECIP_DEVICE,
> +                              0, type, (char *)string, strlen(string) + 1,
> +                              USB_CTRL_SET_TIMEOUT);
> +}
> +
> +static int cros_aoa_probe(struct usb_interface *intf,
> +                         const struct usb_device_id *id)
> +{
> +       int rv;
> +       u16 aoa_protocol;
> +       struct usb_device *udev = interface_to_usbdev(intf);
> +
> +       rv = usb_control_msg(udev, usb_rcvctrlpipe(udev, 0), AOA_GET_PROTOCOL,
> +                            USB_DIR_IN | USB_TYPE_VENDOR | USB_RECIP_DEVICE,
> +                            0, 0, &aoa_protocol, sizeof(aoa_protocol),
> +                            USB_CTRL_GET_TIMEOUT);
> +       if (rv < 0 && rv != -EPROTO)
> +               goto fail;
> +       if (rv != sizeof(aoa_protocol) || aoa_protocol < 1) {
> +               dev_err(&intf->dev, "bound device does not support AOA?\n");
> +               rv = -ENODEV;
> +               goto fail;
> +       }
> +
> +       if ((rv = set_string(udev, AOA_STR_MANUFACTURER, CROS_MANUF)) < 0 ||
> +           (rv = set_string(udev, AOA_STR_MODEL, CROS_MODEL)) < 0 ||
> +           (rv = set_string(udev, AOA_STR_DESCRIPTION, CROS_DESC)) < 0 ||
> +           (rv = set_string(udev, AOA_STR_VERSION, CROS_VERSION)) < 0 ||
> +           (rv = set_string(udev, AOA_STR_URI, CROS_URI)) < 0)
> +               goto fail;
> +
> +       rv = usb_control_msg(udev, usb_sndctrlpipe(udev, 0), AOA_START,
> +                            USB_DIR_OUT | USB_TYPE_VENDOR | USB_RECIP_DEVICE,
> +                            0, 0, NULL, 0, USB_CTRL_SET_TIMEOUT);
> +
> +       if (!rv) {
> +               dev_info(&intf->dev, "switching to AOA mode\n");
> +               usb_stor_cros_aoa_bind_busnum = udev->bus->busnum;
> +               usb_stor_cros_aoa_bind_route = udev->route;
> +               return 0;
> +       }
> +
> +fail:  dev_err(&intf->dev, "probe error %d\n", rv);
> +       return rv;
> +}
> +
> +static void cros_aoa_disconnect(struct usb_interface *intf)
> +{
> +       /* nothing to do -- we expect this to happen right after probe() */
> +}
> +
> +static struct usb_driver cros_aoa_stub_driver = {
> +       .name =         DRV_NAME,
> +       .probe =        cros_aoa_probe,
> +       .disconnect =   cros_aoa_disconnect,
> +       .id_table =     cros_aoa_ids,
> +};
> +
> +static int __init cros_aoa_init(void)
> +{
> +       if (!bind || sscanf(bind, "%hx:%hx", &cros_aoa_ids[0].idVendor,
> +                                            &cros_aoa_ids[0].idProduct) != 2)
> +               return -ENODEV;
> +       pr_info(DRV_NAME ": bound to USB device %4x:%4x\n",
> +               cros_aoa_ids[0].idVendor, cros_aoa_ids[0].idProduct);
> +       return usb_register(&cros_aoa_stub_driver);
> +}
> +
> +static void __exit cros_aoa_exit(void)
> +{
> +       usb_deregister(&cros_aoa_stub_driver);
> +}
> +
> +module_init(cros_aoa_init);
> +module_exit(cros_aoa_exit);
> diff --git a/drivers/usb/storage/initializers.c b/drivers/usb/storage/initializers.c
> index f8f9ce8dc7102..3056db79cd1d9 100644
> --- a/drivers/usb/storage/initializers.c
> +++ b/drivers/usb/storage/initializers.c
> @@ -92,3 +92,37 @@ int usb_stor_huawei_e220_init(struct us_data *us)
>         usb_stor_dbg(us, "Huawei mode set result is %d\n", result);
>         return 0;
>  }
> +
> +#if defined(CONFIG_USB_STORAGE_CROS_AOA) || \
> +               defined(CONFIG_USB_STORAGE_CROS_AOA_MODULE)
> +/*
> + * Our VID/PID match grabs any Android device that was switched into Android
> + * Open Accessory mode. We only want to bind to the one that was switched by the
> + * ums-cros-aoa driver. There's no 100% way to identify the same device again
> + * (because it changes all descriptors), but checking that it is on the same bus
> + * with the same topology route should be a pretty good heuristic.
> + */
> +int usb_stor_cros_aoa_bind_busnum = -1;
> +EXPORT_SYMBOL(usb_stor_cros_aoa_bind_busnum);
> +u32 usb_stor_cros_aoa_bind_route;
> +EXPORT_SYMBOL(usb_stor_cros_aoa_bind_route);
> +
> +int usb_stor_cros_aoa_validate(struct us_data *us)
> +{
> +       if (us->pusb_dev->bus->busnum != usb_stor_cros_aoa_bind_busnum ||
> +           us->pusb_dev->route != usb_stor_cros_aoa_bind_route) {
> +               dev_info(&us->pusb_intf->dev,
> +                        "ums-cros-aoa ignoring unknown AOA device\n");
> +               return -ENODEV;
> +       }
> +
> +       /*
> +        * Only interface 0 connects to the AOA app. Android devices that have
> +        * ADB enabled also export an interface 1. We don't want it.
> +        */
> +       if (us->pusb_intf->cur_altsetting->desc.bInterfaceNumber != 0)
> +               return -ENODEV;
> +
> +       return 0;
> +}
> +#endif /* defined(CONFIG_USB_STORAGE_CROS_AOA) || ... */
> diff --git a/drivers/usb/storage/initializers.h b/drivers/usb/storage/initializers.h
> index 2dbf9c7d97492..35fe9ef3247d6 100644
> --- a/drivers/usb/storage/initializers.h
> +++ b/drivers/usb/storage/initializers.h
> @@ -37,3 +37,7 @@ int usb_stor_ucr61s2b_init(struct us_data *us);
>
>  /* This places the HUAWEI E220 devices in multi-port mode */
>  int usb_stor_huawei_e220_init(struct us_data *us);
> +
> +extern int usb_stor_cros_aoa_bind_busnum;
> +extern u32 usb_stor_cros_aoa_bind_route;
> +int usb_stor_cros_aoa_validate(struct us_data *us);
> diff --git a/drivers/usb/storage/unusual_devs.h b/drivers/usb/storage/unusual_devs.h
> index ea0d27a94afe0..45fe9bbc6da18 100644
> --- a/drivers/usb/storage/unusual_devs.h
> +++ b/drivers/usb/storage/unusual_devs.h
> @@ -2259,6 +2259,24 @@ UNUSUAL_DEV( 0x1e74, 0x4621, 0x0000, 0x0000,
>                 USB_SC_DEVICE, USB_PR_DEVICE, NULL,
>                 US_FL_BULK_IGNORE_TAG | US_FL_MAX_SECTORS_64 ),
>
> +/*
> + * Using an Android phone as USB storage back-end for Chrome OS recovery. See
> + * usb/storage/cros-aoa.c for details.
> + */
> +#if defined(CONFIG_USB_STORAGE_CROS_AOA) || \
> +               defined(CONFIG_USB_STORAGE_CROS_AOA_MODULE)
> +UNUSUAL_DEV(  0x18d1, 0x2d00, 0x0000, 0xffff,
> +               "Google",
> +               "Chrome OS Recovery via AOA",
> +               USB_SC_SCSI, USB_PR_BULK, usb_stor_cros_aoa_validate,
> +               US_FL_SINGLE_LUN | US_FL_CAPACITY_OK),
> +UNUSUAL_DEV(  0x18d1, 0x2d01, 0x0000, 0xffff,
> +               "Google",
> +               "Chrome OS Recovery via AOA (with ADB)",
> +               USB_SC_SCSI, USB_PR_BULK, usb_stor_cros_aoa_validate,
> +               US_FL_SINGLE_LUN | US_FL_CAPACITY_OK),
> +#endif /* defined(CONFIG_USB_STORAGE_CROS_AOA) || ... */
> +
>  /* Supplied with some Castlewood ORB removable drives */
>  UNUSUAL_DEV(  0x2027, 0xa001, 0x0000, 0x9999,
>                 "Double-H Technology",
> --
> 2.20.1
>


-- 
Matthew Dharm
Former Maintainer, USB Mass Storage driver for Linux