I think that you have the right answer. The ANSI/ISO/IEC 1999 C standard spells it out fairly well. I should have looked there:
6.7.2.1 Structure and union specifiers
10 ... If enough space remains, ... shall be packed into adjacent bits of the same unit...
OK thanks, that's the info I was hunting for. So it "should be" safe to declare these bitfields differently, without wasting space. I suspect the semantics there changed since C first got bitfields, and I had remembered the earlier one.
Greg, please merge this patch. It updates the "gadget" kerneldoc, removing some (new) warnings, and showing some fields it hadn't previously been showing (due to limitations in docproc). Plus it adds a bit of information about recent changes (new drivers).
- Dave
--- 1.4/Documentation/DocBook/gadget.tmpl Sat Jul 12 11:09:44 2003
+++ edited/Documentation/DocBook/gadget.tmpl Mon Sep 15 10:43:20 2003
@@ -468,6 +468,15 @@
information.
</para>
+<para>For users of Intel's PXA 2xx series processors,
+a <filename>pxa2xx_udc</filename> driver is available.
+</para>
+
+<para>At this writing, there are people at work on drivers in
+this framework for several other USB device controllers,
+with plans to make many of them be widely available.
+</para>
+
<!-- !Edrivers/usb/gadget/net2280.c -->
<para>A partial USB simulator,
@@ -500,7 +509,7 @@
<para>There's an <emphasis>ethernet</emphasis> gadget
driver, which implements one of the most useful
-<emphasis>Communications Device Class</emphasis> models.
+<emphasis>Communications Device Class</emphasis> (CDC) models.
One of the standards for cable modem interoperability even
specifies the use of this ethernet model as one of two
mandatory options.
@@ -509,6 +518,11 @@
It provides access to a network where the gadget's CPU is one host,
which could easily be bridging, routing, or firewalling
access to other networks.
+Since some hardware can't fully implement the CDC Ethernet
+requirements, this driver also implements a "good parts only"
+subset of CDC Ethernet.
+(That subset doesn't advertise itself as CDC Ethernet,
+to avoid creating problems.)
</para>
<para>There is also support for user mode gadget drivers,
@@ -520,6 +534,17 @@
develop and debug user mode drivers, so that once a robust
controller driver is available many applications for it
won't require new kernel mode software.
+</para>
+
+<para>There's a USB Mass Storage class driver, which provides
+a different solution for interoperability with systems such
+as MS-Windows and MacOS.
+That <emphasis>File-backed Storage</emphasis> driver uses a
+file or block device as backing store for a drive,
+like the <filename>loop</filename> driver.
+The USB host uses the BBB, CB, or CBI versions of the mass
+storage class specification, using transparent SCSI commands
+to access the data from the backing store.
</para>
<para>Support for other kinds of gadget is expected to
--- 1.10/include/linux/usb_gadget.h Wed Sep 3 09:02:09 2003
+++ edited/include/linux/usb_gadget.h Wed Sep 17 14:58:48 2003
@@ -72,9 +72,9 @@
unsigned length;
dma_addr_t dma;
- unsigned no_interrupt : 1,
- zero : 1,
- short_not_ok : 1;
+ unsigned no_interrupt:1;
+ unsigned zero:1;
+ unsigned short_not_ok:1;
void (*complete)(struct usb_ep *ep,
struct usb_request *req);
@@ -122,9 +122,11 @@
/**
* struct usb_ep - device side representation of USB endpoint
* @name:identifier for the endpoint, such as "ep-a" or "ep9in-bulk"
+ * @ops: Function pointers used to access hardware-specific operations.
* @ep_list:the gadget's ep_list holds all of its endpoints
- * @maxpacket:the maximum packet size used on this endpoint, as
- * configured when the endpoint was enabled.
+ * @maxpacket:The maximum packet size used on this endpoint. The initial
+ * value can sometimes be reduced (hardware allowing), according to
+ * the endpoint descriptor used to configure the endpoint.
* @driver_data:for use by the gadget driver. all other fields are
* read-only to gadget drivers.
*
@@ -138,7 +140,7 @@
const char *name;
const struct usb_ep_ops *ops;
struct list_head ep_list;
- unsigned maxpacket : 16;
+ unsigned maxpacket:16;
};
/*-------------------------------------------------------------------------*/
@@ -443,18 +445,21 @@
/**
* struct usb_gadget - represents a usb slave device
+ * @ops: Function pointers used to access hardware-specific operations.
* @ep0: Endpoint zero, used when reading or writing responses to
* driver setup() requests
* @ep_list: List of other endpoints supported by the device.
* @speed: Speed of current connection to USB host.
* @name: Identifies the controller hardware type. Used in diagnostics
* and sometimes configuration.
+ * @dev: Driver model state for this abstract device.
*
* Gadgets have a mostly-portable "gadget driver" implementing device
- * functions, handling all usb configurations and interfaces. They
- * also have a hardware-specific driver (accessed through ops vectors),
- * which insulates the gadget driver from hardware details and packages
- * the hardware endpoints through generic i/o queues.
+ * functions, handling all usb configurations and interfaces. Gadget
+ * drivers talk to hardware-specific code indirectly, through ops vectors.
+ * That insulates the gadget driver from hardware details, and packages
+ * the hardware endpoints through generic i/o queues. The "usb_gadget"
+ * and "usb_ep" interfaces provide that insulation from the hardware.
*
* Except for the driver data, all fields in this structure are
* read-only to the gadget driver. That driver data is part of the
@@ -469,10 +474,6 @@
struct list_head ep_list; /* of usb_ep */
enum usb_device_speed speed;
const char *name;
-
- /* use this to allocate dma-coherent buffers or set up
- * dma mappings. or print diagnostics, etc.
- */
struct device dev;
};
@@ -576,6 +577,7 @@
* Called in a context that permits sleeping.
* @suspend: Invoked on USB suspend. May be called in_interrupt.
* @resume: Invoked on USB resume. May be called in_interrupt.
+ * @driver: Driver model state for this driver.
*
* Devices are disabled till a gadget driver successfully bind()s, which
* means the driver will handle setup() requests needed to enumerate (and
