Commit 7c014315 authored Dec 19, 2017 by Mathias Nyman Committed by Greg Kroah-Hartman Jan 09, 2018

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>

parent e142dc1e

include/uapi/linux/usb/ch9.h

+2 −2

Original line number	Diff line number	Diff line
		@@ -1077,9 +1077,9 @@ struct usb_ptm_cap_descriptor {
		#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)

		/-------------------------------------------------------------------------/