Re: [PATCH v1 1/1] usb: gadget: Use correct APIs and data types for UUID handling

["Jó Ágila Bitsch" <jgilab@gmail.com>]

On Wed, Jan 25, 2023 at 3:34 PM Andy Shevchenko
<andriy.shevchenko@linux.intel.com> wrote:
>
> We have two types for UUIDs depending on the byte ordering.
> Instead of explaining how bytes should go over the wire,
> use dedicated APIs and data types. This removes a confusion
> over the byte ordering.

Thanks for pointing this out. I was unaware of the exact UUID
functions, as I'm still quite a newbie here.

I compiled and tested your patch in my test setup and it works perfectly.

>
> Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
> ---
>  drivers/usb/gadget/composite.c | 4 ++--
>  include/linux/usb/webusb.h     | 9 +++------
>  2 files changed, 5 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/usb/gadget/composite.c b/drivers/usb/gadget/composite.c
> index 8e2603688016..fa7dd6cf014d 100644
> --- a/drivers/usb/gadget/composite.c
> +++ b/drivers/usb/gadget/composite.c
> @@ -829,7 +829,7 @@ static int bos_desc(struct usb_composite_dev *cdev)
>         if (cdev->use_webusb) {
>                 struct usb_plat_dev_cap_descriptor *webusb_cap;
>                 struct usb_webusb_cap_data *webusb_cap_data;
> -               uuid_t webusb_uuid = WEBUSB_UUID;
> +               guid_t webusb_uuid = WEBUSB_UUID;
>
>                 webusb_cap = cdev->req->buf + le16_to_cpu(bos->wTotalLength);
>                 webusb_cap_data = (struct usb_webusb_cap_data *) webusb_cap->CapabilityData;
> @@ -841,7 +841,7 @@ static int bos_desc(struct usb_composite_dev *cdev)
>                 webusb_cap->bDescriptorType = USB_DT_DEVICE_CAPABILITY;
>                 webusb_cap->bDevCapabilityType = USB_PLAT_DEV_CAP_TYPE;
>                 webusb_cap->bReserved = 0;
> -               export_uuid(webusb_cap->UUID, &webusb_uuid);
> +               export_guid(webusb_cap->UUID, &webusb_uuid);
>
>                 if (cdev->bcd_webusb_version != 0)
>                         webusb_cap_data->bcdVersion = cpu_to_le16(cdev->bcd_webusb_version);
> diff --git a/include/linux/usb/webusb.h b/include/linux/usb/webusb.h
> index b430d84357f3..fe43020b4a48 100644
> --- a/include/linux/usb/webusb.h
> +++ b/include/linux/usb/webusb.h
> @@ -11,15 +11,12 @@
>  #include "uapi/linux/usb/ch9.h"
>
>  /*
> - * little endian PlatformCapablityUUID for WebUSB
> + * Little Endian PlatformCapablityUUID for WebUSB
>   * 3408b638-09a9-47a0-8bfd-a0768815b665
> - * to identify Platform Device Capability descriptors as referring to WebUSB
> - *
> - * the UUID above MUST be sent over the wire as the byte sequence:
> - * {0x38, 0xB6, 0x08, 0x34, 0xA9, 0x09, 0xA0, 0x47, 0x8B, 0xFD, 0xA0, 0x76, 0x88, 0x15, 0xB6, 0x65}.

This is actually explicitly spelled out this way in the specification:
https://wicg.github.io/webusb/#webusb-platform-capability-descriptor

But I agree, the way you rewrote it is much clearer!

> + * to identify Platform Device Capability descriptors as referring to WebUSB.
>   */
>  #define WEBUSB_UUID \
> -       UUID_INIT(0x38b60834, 0xa909, 0xa047, 0x8b, 0xfd, 0xa0, 0x76, 0x88, 0x15, 0xb6, 0x65)
> +       GUID_INIT(0x3408b638, 0x09a9, 0x47a0, 0x8b, 0xfd, 0xa0, 0x76, 0x88, 0x15, 0xb6, 0x65)

Yes, this is definitely more readable.

>
>  /*
>   * WebUSB Platform Capability data
> --
> 2.39.0
>