ssi: xilinx_spips: Skip spi bus update for a few register writes

A few configuration register writes need not update the spi bus state, so just
return after the register write.

Signed-off-by: Sai Pavan Boddu <sai.pavan.boddu@xilinx.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Reviewed-by: Francisco Iglesias <frasse.iglesias@gmail.com>
Tested-by: Francisco Iglesias <frasse.iglesias@gmail.com>
Reviewed-by: Edgar E. Iglesias <edgar.iglesias@xilinx.com>
Message-id: 1573830705-14579-1-git-send-email-sai.pavan.boddu@xilinx.com
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

hw/ssi/xilinx_spips.c

@@ -109,6 +109,7 @@
 #define R_GPIO              (0x30 / 4)
 #define R_LPBK_DLY_ADJ      (0x38 / 4)
 #define R_LPBK_DLY_ADJ_RESET (0x33)
+#define R_IOU_TAPDLY_BYPASS (0x3C / 4)
 #define R_TXD1              (0x80 / 4)
 #define R_TXD2              (0x84 / 4)
 #define R_TXD3              (0x88 / 4)
@@ -139,6 +140,8 @@
 #define R_LQSPI_STS         (0xA4 / 4)
 #define LQSPI_STS_WR_RECVD      (1 << 1)
 
+#define R_DUMMY_CYCLE_EN    (0xC8 / 4)
+#define R_ECO               (0xF8 / 4)
 #define R_MOD_ID            (0xFC / 4)
 
 #define R_GQSPI_SELECT          (0x144 / 4)
@@ -970,6 +973,7 @@ static void xilinx_spips_write(void *opaque, hwaddr addr,
 {
     int mask = ~0;
     XilinxSPIPS *s = opaque;
+    bool try_flush = true;
 
     DB_PRINT_L(0, "addr=" TARGET_FMT_plx " = %x\n", addr, (unsigned)value);
     addr >>= 2;
@@ -1019,13 +1023,23 @@ static void xilinx_spips_write(void *opaque, hwaddr addr,
         tx_data_bytes(&s->tx_fifo, (uint32_t)value, 3,
                       s->regs[R_CONFIG] & R_CONFIG_ENDIAN);
         goto no_reg_update;
+    /* Skip SPI bus update for below registers writes */
+    case R_GPIO:
+    case R_LPBK_DLY_ADJ:
+    case R_IOU_TAPDLY_BYPASS:
+    case R_DUMMY_CYCLE_EN:
+    case R_ECO:
+        try_flush = false;
+        break;
     }
     s->regs[addr] = (s->regs[addr] & ~mask) | (value & mask);
 no_reg_update:
-    xilinx_spips_update_cs_lines(s);
-    xilinx_spips_check_flush(s);
-    xilinx_spips_update_cs_lines(s);
-    xilinx_spips_update_ixr(s);
+    if (try_flush) {
+        xilinx_spips_update_cs_lines(s);
+        xilinx_spips_check_flush(s);
+        xilinx_spips_update_cs_lines(s);
+        xilinx_spips_update_ixr(s);
+    }
 }
 
 static const MemoryRegionOps spips_ops = {