hw/sd/allwinner-sdhost: Correctly byteswap descriptor fields

In allwinner_sdhost_process_desc() we just read directly from
guest memory into a host TransferDescriptor struct and back.
This only works on little-endian hosts. Abstract the reading
and writing of descriptors into functions that handle the
byte-swapping so that TransferDescriptor structs as seen by
the rest of the code are always in host-order.

This fixes a failure of one of the avocado tests on s390.

Cc: qemu-stable@nongnu.org
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-id: 20230424165053.1428857-2-peter.maydell@linaro.org

hw/sd/allwinner-sdhost.c

@@ -302,6 +302,30 @@ static void allwinner_sdhost_auto_stop(AwSdHostState *s)
     }
 }
 
+static void read_descriptor(AwSdHostState *s, hwaddr desc_addr,
+                            TransferDescriptor *desc)
+{
+    uint32_t desc_words[4];
+    dma_memory_read(&s->dma_as, desc_addr, &desc_words, sizeof(desc_words),
+                    MEMTXATTRS_UNSPECIFIED);
+    desc->status = le32_to_cpu(desc_words[0]);
+    desc->size = le32_to_cpu(desc_words[1]);
+    desc->addr = le32_to_cpu(desc_words[2]);
+    desc->next = le32_to_cpu(desc_words[3]);
+}
+
+static void write_descriptor(AwSdHostState *s, hwaddr desc_addr,
+                             const TransferDescriptor *desc)
+{
+    uint32_t desc_words[4];
+    desc_words[0] = cpu_to_le32(desc->status);
+    desc_words[1] = cpu_to_le32(desc->size);
+    desc_words[2] = cpu_to_le32(desc->addr);
+    desc_words[3] = cpu_to_le32(desc->next);
+    dma_memory_write(&s->dma_as, desc_addr, &desc_words, sizeof(desc_words),
+                     MEMTXATTRS_UNSPECIFIED);
+}
+
 static uint32_t allwinner_sdhost_process_desc(AwSdHostState *s,
                                               hwaddr desc_addr,
                                               TransferDescriptor *desc,
@@ -312,9 +336,7 @@ static uint32_t allwinner_sdhost_process_desc(AwSdHostState *s,
     uint32_t num_bytes = max_bytes;
     uint8_t buf[1024];
 
-    /* Read descriptor */
-    dma_memory_read(&s->dma_as, desc_addr, desc, sizeof(*desc),
-                    MEMTXATTRS_UNSPECIFIED);
+    read_descriptor(s, desc_addr, desc);
     if (desc->size == 0) {
         desc->size = klass->max_desc_size;
     } else if (desc->size > klass->max_desc_size) {
@@ -356,8 +378,7 @@ static uint32_t allwinner_sdhost_process_desc(AwSdHostState *s,
 
     /* Clear hold flag and flush descriptor */
     desc->status &= ~DESC_STATUS_HOLD;
-    dma_memory_write(&s->dma_as, desc_addr, desc, sizeof(*desc),
-                     MEMTXATTRS_UNSPECIFIED);
+    write_descriptor(s, desc_addr, desc);
 
     return num_done;
 }