diff options
Diffstat (limited to 'include/linux/usb')
| -rw-r--r-- | include/linux/usb/ch9.h | 22 |
1 files changed, 18 insertions, 4 deletions
diff --git a/include/linux/usb/ch9.h b/include/linux/usb/ch9.h index 245c7253122..1122a6c2c1a 100644 --- a/include/linux/usb/ch9.h +++ b/include/linux/usb/ch9.h @@ -1,8 +1,9 @@ /* - * This file holds USB constants and structures that are needed for USB - * device APIs. These are used by the USB device model, which is defined - * in chapter 9 of the USB 2.0 specification. Linux has several APIs in C - * that need these: + * This file holds USB constants and structures that are needed for + * USB device APIs. These are used by the USB device model, which is + * defined in chapter 9 of the USB 2.0 specification and in the + * Wireless USB 1.0 (spread around). Linux has several APIs in C that + * need these: * * - the master/host side Linux-USB kernel driver API; * - the "usbfs" user space API; and @@ -14,6 +15,19 @@ * * There's also "Wireless USB", using low power short range radios for * peripheral interconnection but otherwise building on the USB framework. + * + * Note all descriptors are declared '__attribute__((packed))' so that: + * + * [a] they never get padded, either internally (USB spec writers + * probably handled that) or externally; + * + * [b] so that accessing bigger-than-a-bytes fields will never + * generate bus errors on any platform, even when the location of + * its descriptor inside a bundle isn't "naturally aligned", and + * + * [c] for consistency, removing all doubt even when it appears to + * someone that the two other points are non-issues for that + * particular descriptor type. */ #ifndef __LINUX_USB_CH9_H |