[ot] hw/opentitan: spi_device: discard all packets in failed transaction

If one packet in a transaction triggers an error and needs discarding,
we must continue discarding the remaining packets until CS is released.

Signed-off-by: James Wainwright <[email protected]>

Author: jwnrt

hw/opentitan/ot_spi_device.c

@@ -2,6 +2,7 @@
  * QEMU OpenTitan SPI Device controller
  *
  * Copyright (c) 2023-2025 Rivos, Inc.
+ * Copyright (c) 2025 lowRISC contributors.
  *
  * Author(s):
  *  Emmanuel Blot <[email protected]>
@@ -379,6 +380,7 @@ typedef enum {
     SPI_BUS_TPM,
     SPI_BUS_DISCARD,
     SPI_BUS_ERROR,
+    SPI_BUS_DISCARD_PACKET,
 } OtSpiBusState;
 
 typedef enum {
@@ -641,6 +643,7 @@ static const char *BUS_STATE_NAMES[] = {
     STATE_NAME_ENTRY(SPI_BUS_TPM),
     STATE_NAME_ENTRY(SPI_BUS_DISCARD),
     STATE_NAME_ENTRY(SPI_BUS_ERROR),
+    STATE_NAME_ENTRY(SPI_BUS_DISCARD_PACKET),
 };
 
 static const char *FLASH_STATE_NAMES[] = {
@@ -2028,6 +2031,12 @@ static void ot_spi_device_chr_handle_header(OtSPIDeviceState *s)
         return;
     }
 
+    /* discard the packet if we're within a failed transaction */
+    if (s->bus.state == SPI_BUS_DISCARD_PACKET) {
+        BUS_CHANGE_STATE(s, DISCARD);
+        return;
+    }
+
     /* @todo: Check that the tpm chip-select was assigned.*/
     if (ot_spi_device_is_tpm_enabled(s)) {
         ot_spi_device_tpm_init_buffers(s);
@@ -2242,6 +2251,7 @@ static int ot_spi_device_chr_can_receive(void *opaque)
     unsigned length = 0u;
 
     switch (bus->state) {
+    case SPI_BUS_DISCARD_PACKET:
     case SPI_BUS_IDLE:
         length = fifo8_num_free(&bus->chr_fifo);
         break;
@@ -2274,6 +2284,7 @@ static void ot_spi_device_chr_receive(void *opaque, const uint8_t *buf,
 
     switch (bus->state) {
     case SPI_BUS_IDLE:
+    case SPI_BUS_DISCARD_PACKET:
         g_assert(size <= fifo8_num_free(&bus->chr_fifo));
         while (size--) {
             fifo8_push(&bus->chr_fifo, *buf++);
@@ -2298,12 +2309,33 @@ static void ot_spi_device_chr_receive(void *opaque, const uint8_t *buf,
         break;
     }
 
-    if (!bus->byte_count) {
-        if (bus->release) {
-            ot_spi_device_release(s);
-        } else {
-            BUS_CHANGE_STATE(s, IDLE);
-        }
+    if (bus->byte_count) {
+        /* there is more to process in this state */
+        return;
+    }
+
+    if (bus->release) {
+        /* final packet in transaction, release CS */
+        ot_spi_device_release(s);
+        return;
+    }
+
+    /*
+     * more packets to process in transaction, prepare to receive another header
+     */
+    switch (bus->state) {
+    case SPI_BUS_IDLE:
+    case SPI_BUS_FLASH:
+    case SPI_BUS_DISCARD_PACKET:
+        BUS_CHANGE_STATE(s, IDLE);
+        break;
+    case SPI_BUS_DISCARD:
+    case SPI_BUS_ERROR:
+        BUS_CHANGE_STATE(s, DISCARD_PACKET);
+        break;
+    default:
+        g_assert_not_reached();
+        break;
     }
 }