[RFC PATCH v6 07/11] hw/ssi: imx_spi: Rework imx_spi_write() to handle block disabled

[Philippe Mathieu-Daudé]

When the block is disabled, only the ECSPI_CONREG register can
be modified. Setting the EN bit enabled the device, clearing it
"disables the block and resets the internal logic with the
exception of the ECSPI_CONREG" register.

Move the imx_spi_is_enabled() check earlier.

Ref: i.MX 6DQ Applications Processor Reference Manual (IMX6DQRM),
     chapter 21.7.3: Control Register (ECSPIx_CONREG)

Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
---
 hw/ssi/imx_spi.c | 25 +++++++++++++++----------
 1 file changed, 15 insertions(+), 10 deletions(-)

diff --git a/hw/ssi/imx_spi.c b/hw/ssi/imx_spi.c
index 7ac9da0f1d2..801daa5cbfa 100644
--- a/hw/ssi/imx_spi.c
+++ b/hw/ssi/imx_spi.c
@@ -321,6 +321,20 @@ static void imx_spi_write(void *opaque, hwaddr offset, 
uint64_t value,
 
     trace_imx_spi_write(index, imx_spi_reg_name(index), value);
 
+    if (!imx_spi_is_enabled(s)) {
+        /* Block is disabled */
+        if (index != ECSPI_CONREG) {
+            /* Ignore access */
+            return;
+        }
+        s->regs[ECSPI_CONREG] = value;
+        if (value & ECSPI_CONREG_EN) {
+            /* Keep disabled */
+            return;
+        }
+        /* Enable the block */
+        imx_spi_reset(DEVICE(s));
+    }
 
     switch (index) {
     case ECSPI_RXDATA:
@@ -328,10 +342,7 @@ static void imx_spi_write(void *opaque, hwaddr offset, 
uint64_t value,
                       TYPE_IMX_SPI, __func__);
         break;
     case ECSPI_TXDATA:
-        if (!imx_spi_is_enabled(s)) {
-            /* Ignore writes if device is disabled */
-            break;
-        } else if (fifo32_is_full(&s->tx_fifo)) {
+        if (fifo32_is_full(&s->tx_fifo)) {
             /* Ignore writes if queue is full */
             break;
         }
@@ -357,12 +368,6 @@ static void imx_spi_write(void *opaque, hwaddr offset, 
uint64_t value,
     case ECSPI_CONREG:
         s->regs[ECSPI_CONREG] = value;
 
-        if (!imx_spi_is_enabled(s)) {
-            /* device is disabled, so this is a reset */
-            imx_spi_reset(DEVICE(s));
-            return;
-        }
-
         if (imx_spi_channel_is_master(s)) {
             uint32_t change_mask = s->regs[index] ^ value;
             int i;
-- 
2.26.2