scsi: esp: clean up handle_ti/esp_do_dma if s->do_cmd

Avoid duplicated code between esp_do_dma and handle_ti.  esp_do_dma
has the same code that handle_ti contains after the call to esp_do_dma;
but the code in handle_ti is never reached because it is in an "else if".
Remove the else and also the pointless return.

esp_do_dma also has a partially dead assignment of the to_device
variable.  Sink it to the point where it's actually used.

Finally, assert that the other caller of esp_do_dma (esp_transfer_data)
only transfers data and not a command.  This is true because get_cmd
cancels the old request synchronously before its caller handle_satn_stop
sets do_cmd to 1.

Reviewed-by: Laszlo Ersek <lersek@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
(cherry picked from commit 7f0b6e1)
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>

hw/scsi/esp.c

@@ -245,15 +245,10 @@ static void esp_do_dma(ESPState *s)
     uint32_t len;
     int to_device;
 
-    to_device = (s->ti_size < 0);
     len = s->dma_left;
     if (s->do_cmd) {
         trace_esp_do_dma(s->cmdlen, len);
         s->dma_memory_read(s->dma_opaque, &s->cmdbuf[s->cmdlen], len);
-        s->ti_size = 0;
-        s->cmdlen = 0;
-        s->do_cmd = 0;
-        do_cmd(s, s->cmdbuf);
         return;
     }
     if (s->async_len == 0) {
@@ -263,6 +258,7 @@ static void esp_do_dma(ESPState *s)
     if (len > s->async_len) {
         len = s->async_len;
     }
+    to_device = (s->ti_size < 0);
     if (to_device) {
         s->dma_memory_read(s->dma_opaque, s->async_buf, len);
     } else {
@@ -318,6 +314,7 @@ void esp_transfer_data(SCSIRequest *req, uint32_t len)
 {
     ESPState *s = req->hba_private;
 
+    assert(!s->do_cmd);
     trace_esp_transfer_data(s->dma_left, s->ti_size);
     s->async_len = len;
     s->async_buf = scsi_req_get_buf(req);
@@ -358,13 +355,13 @@ static void handle_ti(ESPState *s)
         s->dma_left = minlen;
         s->rregs[ESP_RSTAT] &= ~STAT_TC;
         esp_do_dma(s);
-    } else if (s->do_cmd) {
+    }
+    if (s->do_cmd) {
         trace_esp_handle_ti_cmd(s->cmdlen);
         s->ti_size = 0;
         s->cmdlen = 0;
         s->do_cmd = 0;
         do_cmd(s, s->cmdbuf);
-        return;
     }
 }