greybus: interface: Extract and store Interface feature byte

The Interface description in the Greybus specification contains a
'features' field which is currently not implemented on the AP side. The
Interface features field provides information on optional attributes of an
Interface as a bitmask. Currently only GREYBUS_INTERFACE_FEATURE_TIMESYNC
is implemented in the specification but, the expectation is that other
feature flags will be added over time.

This patch adds support to extract the feature byte communicated in the
features field of the Interface Descriptor header and extends struct
interface to contain a features field through which any user with a pointer
to struct interface may interrogate the features of an Interface.

This is a necessary pre-cursor for TimeSync to ensure only Interfaces which
declare GREYBUS_INTERFACE_FEATURE_TIMESYNC will be included when we go
through the process of FrameTime synchronization.

Signed-off-by: Bryan O'Donoghue <bryan.odonoghue@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>

drivers/staging/greybus/greybus_manifest.h

@@ -81,6 +81,10 @@ enum greybus_class_type {
 	GREYBUS_CLASS_VENDOR		= 0xff,
 };
 
+enum {
+	GREYBUS_INTERFACE_FEATURE_TIMESYNC = BIT(0),
+};
+
 /*
  * The string in a string descriptor is not NUL-terminated.  The
  * size of the descriptor will be rounded up to a multiple of 4
@@ -99,7 +103,8 @@ struct greybus_descriptor_string {
 struct greybus_descriptor_interface {
 	__u8	vendor_stringid;
 	__u8	product_stringid;
-	__u8	pad[2];
+	__u8	features;
+	__u8	pad;
 } __packed;
 
 /*

drivers/staging/greybus/interface.h

@@ -23,6 +23,7 @@ struct gb_interface {
 	struct list_head manifest_descs;
 	u8 interface_id;	/* Physical location within the Endo */
 	u8 device_id;
+	u8 features;		/* Feature flags set in the manifest */
 
 	u32 ddbl1_manufacturer_id;
 	u32 ddbl1_product_id;

drivers/staging/greybus/manifest.c

@@ -398,6 +398,9 @@ static bool gb_manifest_parse_interface(struct gb_interface *intf,
 		goto out_free_vendor_string;
 	control->product_string = str;
 
+	/* Assign feature flags communicated via manifest */
+	intf->features = desc_intf->features;
+
 	/* Release the interface descriptor, now that we're done with it */
 	release_manifest_descriptor(interface_desc);