esp: add support for unaligned accesses

When the MacOS toolbox ROM transfers data from a target device to an unaligned
memory address, the first/last byte of a 16-bit transfer needs to be handled
separately. This means that the first byte is preloaded into the FIFO before
the transfer, or the last byte remains in the FIFO after the transfer.

The result of this is that the PDMA routines must be updated so that the FIFO
is loaded/unloaded if the last 16-bit word is used (rather than the last byte)
and any remaining byte from a FIFO wraparound is handled correctly.

Signed-off-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
Reviewed-by: Laurent Vivier <laurent@vivier.eu>
Message-Id: <20210304221103.6369-43-mark.cave-ayland@ilande.co.uk>

hw/scsi/esp.c

@@ -498,11 +498,22 @@ static void do_dma_pdma_cb(ESPState *s)
 
     if (to_device) {
         /* Copy FIFO data to device */
-        len = MIN(fifo8_num_used(&s->fifo), ESP_FIFO_SZ);
+        len = MIN(s->async_len, ESP_FIFO_SZ);
+        len = MIN(len, fifo8_num_used(&s->fifo));
         memcpy(s->async_buf, fifo8_pop_buf(&s->fifo, len, &n), len);
-        s->async_buf += len;
-        s->async_len -= len;
-        s->ti_size += len;
+        s->async_buf += n;
+        s->async_len -= n;
+        s->ti_size += n;
+
+        if (n < len) {
+            /* Unaligned accesses can cause FIFO wraparound */
+            len = len - n;
+            memcpy(s->async_buf, fifo8_pop_buf(&s->fifo, len, &n), len);
+            s->async_buf += n;
+            s->async_len -= n;
+            s->ti_size += n;
+        }
+
         if (s->async_len == 0) {
             scsi_req_continue(s->current_req);
             return;
@@ -526,12 +537,18 @@ static void do_dma_pdma_cb(ESPState *s)
 
         if (esp_get_tc(s) != 0) {
             /* Copy device data to FIFO */
-            len = MIN(s->async_len, fifo8_num_free(&s->fifo));
+            len = MIN(s->async_len, esp_get_tc(s));
+            len = MIN(len, fifo8_num_free(&s->fifo));
             fifo8_push_all(&s->fifo, s->async_buf, len);
             s->async_buf += len;
             s->async_len -= len;
             s->ti_size -= len;
             esp_set_tc(s, esp_get_tc(s) - len);
+
+            if (esp_get_tc(s) == 0) {
+                /* Indicate transfer to FIFO is complete */
+                 s->rregs[ESP_RSTAT] |= STAT_TC;
+            }
             return;
         }
 
@@ -606,12 +623,29 @@ static void esp_do_dma(ESPState *s)
         if (s->dma_memory_write) {
             s->dma_memory_write(s->dma_opaque, s->async_buf, len);
         } else {
+            /* Adjust TC for any leftover data in the FIFO */
+            if (!fifo8_is_empty(&s->fifo)) {
+                esp_set_tc(s, esp_get_tc(s) - fifo8_num_used(&s->fifo));
+            }
+
             /* Copy device data to FIFO */
             len = MIN(len, fifo8_num_free(&s->fifo));
             fifo8_push_all(&s->fifo, s->async_buf, len);
             s->async_buf += len;
             s->async_len -= len;
             s->ti_size -= len;
+
+            /*
+             * MacOS toolbox uses a TI length of 16 bytes for all commands, so
+             * commands shorter than this must be padded accordingly
+             */
+            if (len < esp_get_tc(s) && esp_get_tc(s) <= ESP_FIFO_SZ) {
+                while (fifo8_num_used(&s->fifo) < ESP_FIFO_SZ) {
+                    esp_fifo_push(s, 0);
+                    len++;
+                }
+            }
+
             esp_set_tc(s, esp_get_tc(s) - len);
             s->pdma_cb = do_dma_pdma_cb;
             esp_raise_drq(s);
@@ -1160,7 +1194,7 @@ static void sysbus_esp_pdma_write(void *opaque, hwaddr addr,
         break;
     }
     dmalen = esp_get_tc(s);
-    if (dmalen == 0 || fifo8_is_full(&s->fifo)) {
+    if (dmalen == 0 || fifo8_num_free(&s->fifo) < 2) {
         s->pdma_cb(s);
     }
 }
@@ -1183,7 +1217,7 @@ static uint64_t sysbus_esp_pdma_read(void *opaque, hwaddr addr,
         val = (val << 8) | esp_pdma_read(s);
         break;
     }
-    if (fifo8_is_empty(&s->fifo)) {
+    if (fifo8_num_used(&s->fifo) < 2) {
         s->pdma_cb(s);
     }
     return val;