[RESEND PATCH] mailbox: Add dummy mailbox API implementation

[Daniel Baluta <daniel.baluta@oss.nxp.com>]

From: Daniel Baluta <daniel.baluta@nxp.com>

There are users of mailbox API that could be enabled
via COMPILE_TEST without select CONFIG_MAILBOX.

In such cases we got compilation errors, like these:

ld: drivers/firmware/imx/imx-scu.o: in function `imx_scu_probe':
imx-scu.c:(.text+0x25e): undefined reference to
`mbox_request_channel_byname'
ld: drivers/firmware/imx/imx-scu.o: in function `imx_scu_call_rpc':
imx-scu.c:(.text+0x4b8): undefined reference to `mbox_send_message'
ld: drivers/firmware/imx/imx-scu-irq.o: in function
`imx_scu_enable_general_irq_channel':
imx-scu-irq.c:(.text+0x34d): undefined reference to
`mbox_request_channel_byname'

Fix this by implementing dummy mailbox API when CONFIG_MAILBOX is not
set.

Reported-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Daniel Baluta <daniel.baluta@nxp.com>
---
resend adding Jassi's email

 include/linux/mailbox_client.h | 34 ++++++++++++++++++++++++++++++++++
 1 file changed, 34 insertions(+)

diff --git a/include/linux/mailbox_client.h b/include/linux/mailbox_client.h
index 65229a45590f..ab5d130f0b5c 100644
--- a/include/linux/mailbox_client.h
+++ b/include/linux/mailbox_client.h
@@ -37,6 +37,7 @@ struct mbox_client {
 	void (*tx_done)(struct mbox_client *cl, void *mssg, int r);
 };
 
+#ifdef CONFIG_MAILBOX
 struct mbox_chan *mbox_request_channel_byname(struct mbox_client *cl,
 					      const char *name);
 struct mbox_chan *mbox_request_channel(struct mbox_client *cl, int index);
@@ -46,4 +47,37 @@ void mbox_client_txdone(struct mbox_chan *chan, int r); /* atomic */
 bool mbox_client_peek_data(struct mbox_chan *chan); /* atomic */
 void mbox_free_channel(struct mbox_chan *chan); /* may sleep */
 
+#else
+static inline
+struct mbox_chan *mbox_request_channel_byname(struct mbox_client *cl,
+					      const char *name)
+{
+	return ERR_PTR(-ENOTSUPP);
+}
+
+static inline
+struct mbox_chan *mbox_request_channel(struct mbox_client *cl, int index)
+{
+	return ERR_PTR(-ENOTSUPP);
+}
+
+static inline int mbox_send_message(struct mbox_chan *chan, void *mssg)
+{
+	return -ENOTSUPP;
+}
+
+static inline int mbox_flush(struct mbox_chan *chan, unsigned long timeout)
+{
+	return -ENOTSUPP;
+}
+
+static inline void mbox_client_txdone(struct mbox_chan *chan, int r) { }
+
+static inline bool mbox_client_peek_data(struct mbox_chan *chan)
+{
+	return false;
+}
+
+static inline void mbox_free_channel(struct mbox_chan *chan) { }
+#endif
 #endif /* __MAILBOX_CLIENT_H */
-- 
2.17.1