[PATCH v4 10/12] usb: xhci: dbc: add handshake between debug target and host

[Lu Baolu <baolu.lu@linux.intel.com>]

After DbC setup, debug target needs to wait until tty driver and
application (e.g. mincom) on debug taget start.  Otherwise, out
messages might be ignored.

This patch adds a ping/pong mechanism between debug target and
host. Debug target will be waiting there until user presses 'Y'
or 'y' in the tty application.

Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
---
 drivers/usb/early/xhci-dbc.c | 27 +++++++++++++++++++++++++++
 1 file changed, 27 insertions(+)

diff --git a/drivers/usb/early/xhci-dbc.c b/drivers/usb/early/xhci-dbc.c
index 68a7139..b75c523 100644
--- a/drivers/usb/early/xhci-dbc.c
+++ b/drivers/usb/early/xhci-dbc.c
@@ -32,6 +32,9 @@
 static struct xdbc_state xdbc_stat;
 static struct xdbc_state *xdbcp = &xdbc_stat;
 
+static int early_xdbc_read(struct console *con, char *str, unsigned n);
+static void early_xdbc_write(struct console *con, const char *str, u32 n);
+
 #ifdef DBC_DEBUG
 #define	XDBC_DEBUG_BUF_SIZE	(PAGE_SIZE * 32)
 #define	MSG_MAX_LINE		128
@@ -873,8 +876,12 @@ int __init early_xdbc_init(char *s)
 {
 	u32 bus = 0, dev = 0, func = 0;
 	unsigned long dbgp_num = 0;
+	char *ping = "Press Y to continue...\n";
+	char pong[64];
+	size_t size;
 	u32 offset;
 	int ret;
+	int retry = 20;
 
 	if (!early_pci_allowed())
 		return -EPERM;
@@ -917,6 +924,21 @@ int __init early_xdbc_init(char *s)
 		return ret;
 	}
 
+	while (retry > 0) {
+		early_xdbc_write(NULL, ping, strlen(ping));
+		size = early_xdbc_read(NULL, pong, 64);
+		if (size > 0) {
+			xdbc_trace("%s: pong message: %s\n", __func__, pong);
+			if (pong[0] == 'Y' || pong[0] == 'y')
+				break;
+		} else {
+			xdbc_trace("%s: pong message error %d\n",
+				__func__, size);
+		}
+
+		retry--;
+	}
+
 	return 0;
 }
 
@@ -1338,6 +1360,11 @@ int xdbc_bulk_write(const char *bytes, int size)
  * Start a bulk-in or bulk-out transfer, wait until transfer completion
  * or error. Return the count of actually transferred bytes or error.
  */
+static int early_xdbc_read(struct console *con, char *str, unsigned n)
+{
+	return xdbc_bulk_read(str, n, 0);
+}
+
 static void early_xdbc_write(struct console *con, const char *str, u32 n)
 {
 	int chunk, ret;
-- 
2.1.4