All commands switching from TRANSFER state to (receiving)DATA
do the same: receive stream of data from the DAT lines. Instead
of duplicating the same code many times, introduce 2 helpers:
- sd_cmd_to_receivingdata() on the I/O line setup the data to
  be received on the data[] buffer,
- sd_generic_write_byte() on the DAT lines to push the data.

Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
---
 hw/sd/sd.c | 28 ++++++++++++++++++++++++++++
 1 file changed, 28 insertions(+)

diff --git a/hw/sd/sd.c b/hw/sd/sd.c
index 2df3c28cb7..7fea0afb62 100644
--- a/hw/sd/sd.c
+++ b/hw/sd/sd.c
@@ -1081,6 +1081,21 @@ static sd_rsp_type_t sd_cmd_unimplemented(SDState *sd, SDRequest req)
     return sd_illegal;
 }
 
+__attribute__((unused))
+static sd_rsp_type_t sd_cmd_to_receivingdata(SDState *sd, SDRequest req,
+                                             uint64_t start, size_t size)
+{
+    if (sd->state != sd_transfer_state) {
+        return sd_invalid_state_for_cmd(sd, req);
+    }
+    sd->state = sd_receivingdata_state;
+    sd->data_start = start;
+    sd->data_offset = 0;
+    /* sd->data[] used as receive buffer */
+    sd->data_size = size ?: sizeof(sd->data);
+    return sd_r1;
+}
+
 static sd_rsp_type_t sd_cmd_to_sendingdata(SDState *sd, SDRequest req,
                                            uint64_t start,
                                            const void *data, size_t size)
@@ -1930,6 +1945,19 @@ send_response:
     return rsplen;
 }
 
+/* Return true when buffer consumed */
+__attribute__((unused))
+static bool sd_generic_write_byte(SDState *sd, uint8_t value)
+{
+    sd->data[sd->data_offset] = value;
+
+    if (++sd->data_offset >= sd->data_size) {
+        sd->state = sd_transfer_state;
+        return true;
+    }
+    return false;
+}
+
 /* Return true when buffer consumed */
 static bool sd_generic_read_byte(SDState *sd, uint8_t *value)
 {
-- 
2.41.0