xilinx_spips: Add automatic start support

SPI has a mode where it automatically starts based on tx fifo
occupancy. Implemented.

Signed-off-by: Peter Crosthwaite <peter.crosthwaite@xilinx.com>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Edgar E. Iglesias <edgar.iglesias@gmail.com>
Message-id: f4e9accb5de87b526fff6ed937f63278db76533b.1369117359.git.peter.crosthwaite@xilinx.com
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

hw/ssi/xilinx_spips.c

diff --git a/hw/ssi/xilinx_spips.c b/hw/ssi/xilinx_spips.c
index cf4c43e..0c04ec9 100644
--- a/hw/ssi/xilinx_spips.c
+++ b/hw/ssi/xilinx_spips.c
@@ -451,7 +451,8 @@
     }
     s->regs[addr] = (s->regs[addr] & ~mask) | (value & mask);
 no_reg_update:
-    if (man_start_com) {
+    if ((man_start_com && s->regs[R_CONFIG] & MAN_START_EN) ||
+            (fifo8_is_empty(&s->tx_fifo) && s->regs[R_CONFIG] & MAN_START_EN)) {
         xilinx_spips_flush_txfifo(s);
     }
     xilinx_spips_update_ixr(s);