esp: correctly accumulate extended messages for PDMA

Commit 799d90d "esp: transition to message out phase after SATN and stop
command" added logic to correctly handle extended messages for DMA requests
but not for PDMA requests.

Apply the same logic in esp_do_dma() to do_dma_pdma_cb() so that extended
messages terminated with a PDMA request are accumulated correctly. This allows
the ESP device to respond correctly to the SDTR negotiation initiated by the
NetBSD ESP driver without causing errors and timeouts on boot.

Signed-off-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
Message-Id: <20210519100803.10293-6-mark.cave-ayland@ilande.co.uk>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

hw/scsi/esp.c

@@ -492,9 +492,26 @@ static void do_dma_pdma_cb(ESPState *s)
         }
 
         s->ti_size = 0;
-        s->do_cmd = 0;
-        do_cmd(s);
-        esp_lower_drq(s);
+        if ((s->rregs[ESP_RSTAT] & 7) == STAT_CD) {
+            /* No command received */
+            if (s->cmdfifo_cdb_offset == fifo8_num_used(&s->cmdfifo)) {
+                return;
+            }
+
+            /* Command has been received */
+            s->do_cmd = 0;
+            do_cmd(s);
+        } else {
+            /*
+             * Extra message out bytes received: update cmdfifo_cdb_offset
+             * and then switch to commmand phase
+             */
+            s->cmdfifo_cdb_offset = fifo8_num_used(&s->cmdfifo);
+            s->rregs[ESP_RSTAT] = STAT_TC | STAT_CD;
+            s->rregs[ESP_RSEQ] = SEQ_CD;
+            s->rregs[ESP_RINTR] |= INTR_BS;
+            esp_raise_irq(s);
+        }
         return;
     }