USB: clarify USB_DT_USB_SSP_CAP_SIZE(ssac) definition
USB_DT_USB_SSP_CAP_SIZE(ssac) gives the size of the SSP capability
descriptor. The descriptor consists of 12 bytes plus a array of
SSA entries.
The number of SSA entries is stored in a SSAC value in the first 12 bytes,
The USB3.1 specification 9.6.2.5 defines SSAC as zero based:
"The number of Sublink Speed Attributes = SSAC + 1." This is not
intuitive and has already caused some confusion.
Make a small modifiaction to the USB_DT_USB_SSP_CAP_SIZE(ssac)
definition to make it a bit clearer
Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
diff --git a/include/uapi/linux/usb/ch9.h b/include/uapi/linux/usb/ch9.h
index c4c79aa3..d5a5cae 100644
--- a/include/uapi/linux/usb/ch9.h
+++ b/include/uapi/linux/usb/ch9.h
@@ -1077,9 +1077,9 @@
#define USB_DT_USB_PTM_ID_SIZE 3
/*
* The size of the descriptor for the Sublink Speed Attribute Count
- * (SSAC) specified in bmAttributes[4:0].
+ * (SSAC) specified in bmAttributes[4:0]. SSAC is zero-based
*/
-#define USB_DT_USB_SSP_CAP_SIZE(ssac) (16 + ssac * 4)
+#define USB_DT_USB_SSP_CAP_SIZE(ssac) (12 + (ssac + 1) * 4)
/*-------------------------------------------------------------------------*/