diff options
Diffstat (limited to 'include/linux')
-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 245c72531228..1122a6c2c1a3 100644 --- a/include/linux/usb/ch9.h +++ b/include/linux/usb/ch9.h | |||
@@ -1,8 +1,9 @@ | |||
1 | /* | 1 | /* |
2 | * This file holds USB constants and structures that are needed for USB | 2 | * This file holds USB constants and structures that are needed for |
3 | * device APIs. These are used by the USB device model, which is defined | 3 | * USB device APIs. These are used by the USB device model, which is |
4 | * in chapter 9 of the USB 2.0 specification. Linux has several APIs in C | 4 | * defined in chapter 9 of the USB 2.0 specification and in the |
5 | * that need these: | 5 | * Wireless USB 1.0 (spread around). Linux has several APIs in C that |
6 | * need these: | ||
6 | * | 7 | * |
7 | * - the master/host side Linux-USB kernel driver API; | 8 | * - the master/host side Linux-USB kernel driver API; |
8 | * - the "usbfs" user space API; and | 9 | * - the "usbfs" user space API; and |
@@ -14,6 +15,19 @@ | |||
14 | * | 15 | * |
15 | * There's also "Wireless USB", using low power short range radios for | 16 | * There's also "Wireless USB", using low power short range radios for |
16 | * peripheral interconnection but otherwise building on the USB framework. | 17 | * peripheral interconnection but otherwise building on the USB framework. |
18 | * | ||
19 | * Note all descriptors are declared '__attribute__((packed))' so that: | ||
20 | * | ||
21 | * [a] they never get padded, either internally (USB spec writers | ||
22 | * probably handled that) or externally; | ||
23 | * | ||
24 | * [b] so that accessing bigger-than-a-bytes fields will never | ||
25 | * generate bus errors on any platform, even when the location of | ||
26 | * its descriptor inside a bundle isn't "naturally aligned", and | ||
27 | * | ||
28 | * [c] for consistency, removing all doubt even when it appears to | ||
29 | * someone that the two other points are non-issues for that | ||
30 | * particular descriptor type. | ||
17 | */ | 31 | */ |
18 | 32 | ||
19 | #ifndef __LINUX_USB_CH9_H | 33 | #ifndef __LINUX_USB_CH9_H |