mailbox: Allow operation without .recv callback

Some shared memory mailboxes may have empty receive operation,
because the data are polled by upper layers directly from the
shared memory region, and there is no completion interrupt or
bit of any sort. Allow empty .recv callback, and if the .recv
callback is empty, exit from mbox_recv() right away, because
any polling for completion here would be meaningless.

Signed-off-by: Marek Vasut <marek.vasut+renesas@mailbox.org>
Reviewed-by: Alice Guo <alice.guo@nxp.com>

diff --git a/drivers/mailbox/mailbox-uclass.c b/drivers/mailbox/mailbox-uclass.c
index 4bf4987ce0a1db957f165dd5726fccdeafb42f8a..fef437a4281ac682804f9bb1093695babadc17ba 100644 (file)
--- a/drivers/mailbox/mailbox-uclass.c
+++ b/drivers/mailbox/mailbox-uclass.c
@@ -132,6 +132,15 @@ int mbox_recv(struct mbox_chan *chan, void *data, ulong timeout_us)
        debug("%s(chan=%p, data=%p, timeout_us=%ld)\n", __func__, chan, data,
              timeout_us);
 
+       /*
+        * Some shared memory mailboxes may have empty receive operation,
+        * because the data are polled by upper layers directly from the
+        * shared memory region, and there is no completion interrupt or
+        * bit of any sort.
+        */
+       if (!ops->recv)
+               return 0;
+
        start_time = timer_get_us();
        /*
         * Account for partial us ticks, but if timeout_us is 0, ensure we