disp: msm: debugfs interface for sde connector to do DSI read

This change implements a new feature to read the cmds response
of the panel from sde connector interface. Sde connector opens
debugfs interface for all the connectors those have support for
cmd receive operation.

Sde connector init module creates rx_cmd debugfs file at
/<debugfs-root>/dri/0/DSI-1/ for DSI-1 connector.
Format for DSI command transfer:
echo "command bytes" > /<debugfs-root/dri/0/DSI-1/rx_cmd
byte-0: the length of received buffer
byte-1: data-type
byte-2: last command. always 0x01
byte-3: channel number
byte-4: flags. MIPI_DSI_MSG_*, must be set to 0xa
byte-5: 0x00
byte-6 and byte-7: command payload length
byte-8 to byte-[8+payload length]: command payload
Example:
echo "0x01 0x06 0x01 0x00 0x0a 0x00 0x00 0x01 0x0a" > rx_cmd
The command receive operations are allowed only if controller
(ex. DSI controller) is in active state.
Read the value of panel response:
cat /<debugfs-root>/dri/0/DSI-1/rx_cmd
returns the value of this command.
nothing - failure, xx xx - success.

Change-Id: I912b65d606e248c7a886d219f4363bf7766ee7b6
Signed-off-by: Yuan Zhao <yzhao@codeaurora.org>

msm/dsi/dsi_display.h

@@ -653,6 +653,17 @@ int dsi_display_cmd_transfer(struct drm_connector *connector,
 		void *display, const char *cmd_buffer,
 		u32 cmd_buf_len);
 
+/**
+ * dsi_display_cmd_receive() - receive response from the panel
+ * @display:            Handle to display.
+ * @cmd_buf:            Command buffer
+ * @cmd_buf_len:        Command buffer length in bytes
+ * @recv_buf:           Receive buffer
+ * @recv_buf_len:       Receive buffer length in bytes
+ */
+int dsi_display_cmd_receive(void *display, const char *cmd_buf,
+			    u32 cmd_buf_len, u8 *recv_buf, u32 recv_buf_len);
+
 /**
  * dsi_display_soft_reset() - perform a soft reset on DSI controller
  * @display:         Handle to display