On 9/26/2013 2:10 AM, Felipe Balbi wrote:
Hi,
(please avoid top-posting)
On Tue, Sep 24, 2013 at 03:00:20PM +0530, Manu Gautam wrote:
Hi Felipe,
I wanted to mention one point with respect to this patch: Below
changes in the functionfs.h to add ss_count (super speed descriptors
count) in desc_header (which is passed from userspace) make the driver
incompatible with existing userspace applications compiled against old
header file. Let me know if that is acceptable. We are using this
driver with Android for adbd (android debug bridge) and these changes
are required to support adb over Super Speed controllers e.g. DWC3
along with changed in adbd to pass SS EP and companion descriptors.
Good you mentioned, it saves me the trouble of reviewing this patch :-)
It's not acceptable to break userspace ABI at all. If you want
SuperSpeed support on function fs, we need to figure out a way to do so
without breaking userspace.
This might mean adding a separate userspace interface to be used with
superspeed. While at that, we might want to add a few bytes of reserved,
unused space in our structures for situations where we need to add more
data into it, just to make it slightly future proof.
Thanks for your reply.
As you suggested we can have a different interface for super speed
which would be optional to workaround ABI compatibility issue.
Let me know if below interface looks fine to you, I will then implement
accordingly:
diff --git a/include/uapi/linux/usb/functionfs.h
b/include/uapi/linux/usb/functionfs.h
index d6b0128..b8cb740 100644
--- a/include/uapi/linux/usb/functionfs.h
+++ b/include/uapi/linux/usb/functionfs.h
@@ -9,8 +9,9 @@
enum {
- FUNCTIONFS_DESCRIPTORS_MAGIC = 1,
- FUNCTIONFS_STRINGS_MAGIC = 2
+ FUNCTIONFS_DESCRIPTORS_MAGIC = 1,
+ FUNCTIONFS_STRINGS_MAGIC = 2,
+ FUNCTIONFS_SS_DESCRIPTORS_MAGIC = 3
};
@@ -60,6 +61,25 @@ struct usb_functionfs_descs_head {
* | 2 | payload | | descriptor's payload |
*/
+struct usb_functionfs_ss_descs_head {
+ __le32 magic;
+ __le32 length;
+ __le32 reserved;
+ __le32 ss_count;
+} __attribute__((packed));
+
+/*
+ * SS Descriptors format:
+ *
+ * | off | name | type | description
|
+ *
|-----+-----------+--------------+--------------------------------------|
+ * | 0 | magic | LE32 | FUNCTIONFS_SS_DESCRIPTORS_MAGIC
|
+ * | 4 | length | LE32 | length of the whole data chunk
|
+ * | 8 | ss_count | LE32 | number of super-speed descriptors
|
+ * | 12 | reserved field
|
+ * | 16 | ss_descrs | Descriptor[] | list of super-speed descriptors
|
+ */
+
struct usb_functionfs_strings_head {
__le32 magic;
__le32 length;
--
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