powerpc/vas: Define vas_win_id()

Define an interface to return a system-wide unique id for a given VAS
window.

The vas_win_id() will be used in a follow-on patch to generate an unique
handle for a user space receive window. Applications can use this handle
to pair send and receive windows for fast thread-wakeup.

The hardware refers to this system-wide unique id as a Partition Send
Window ID which is expected to be used during fault handling. Hence the
"pswid" in the function names.

Signed-off-by: Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/include/asm/vas.h

@@ -167,6 +167,11 @@ int vas_copy_crb(void *crb, int offset);
  */
 int vas_paste_crb(struct vas_window *win, int offset, bool re);
 
+/*
+ * Return a system-wide unique id for the VAS window @win.
+ */
+extern u32 vas_win_id(struct vas_window *win);
+
 /*
  * Return the power bus paste address associated with @win so the caller
  * can map that address into their address space.

arch/powerpc/platforms/powernv/vas-window.c

@@ -1235,3 +1235,12 @@ int vas_win_close(struct vas_window *window)
 	return 0;
 }
 EXPORT_SYMBOL_GPL(vas_win_close);
+
+/*
+ * Return a system-wide unique window id for the window @win.
+ */
+u32 vas_win_id(struct vas_window *win)
+{
+	return encode_pswid(win->vinst->vas_id, win->winid);
+}
+EXPORT_SYMBOL_GPL(vas_win_id);

arch/powerpc/platforms/powernv/vas.h

@@ -447,4 +447,32 @@ static inline u64 read_hvwc_reg(struct vas_window *win,
 	return in_be64(win->hvwc_map+reg);
 }
 
+/*
+ * Encode/decode the Partition Send Window ID (PSWID) for a window in
+ * a way that we can uniquely identify any window in the system. i.e.
+ * we should be able to locate the 'struct vas_window' given the PSWID.
+ *
+ *	Bits	Usage
+ *	0:7	VAS id (8 bits)
+ *	8:15	Unused, 0 (3 bits)
+ *	16:31	Window id (16 bits)
+ */
+static inline u32 encode_pswid(int vasid, int winid)
+{
+	u32 pswid = 0;
+
+	pswid |= vasid << (31 - 7);
+	pswid |= winid;
+
+	return pswid;
+}
+
+static inline void decode_pswid(u32 pswid, int *vasid, int *winid)
+{
+	if (vasid)
+		*vasid = pswid >> (31 - 7) & 0xFF;
+
+	if (winid)
+		*winid = pswid & 0xFFFF;
+}
 #endif /* _VAS_H */