imx_fec: Emulate SHIFT16 in ENETx_RACC

Needed to support latest Linux kernel driver which relies on that
functionality.

Cc: Peter Maydell <peter.maydell@linaro.org>
Cc: Jason Wang <jasowang@redhat.com>
Cc: Philippe Mathieu-Daudé <f4bug@amsat.org>
Cc: qemu-devel@nongnu.org
Cc: qemu-arm@nongnu.org
Cc: yurovsky@gmail.com
Reviewed-by: NPeter Maydell <peter.maydell@linaro.org>
Signed-off-by: NAndrey Smirnov <andrew.smirnov@gmail.com>
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>

hw/net/imx_fec.c

@@ -1037,6 +1037,7 @@ static ssize_t imx_enet_receive(NetClientState *nc, const uint8_t *buf,
     uint8_t *crc_ptr;
     unsigned int buf_len;
     size_t size = len;
+    bool shift16 = s->regs[ENET_RACC] & ENET_RACC_SHIFT16;
 
     FEC_PRINTF("len %d\n", (int)size);
 
@@ -1051,6 +1052,10 @@ static ssize_t imx_enet_receive(NetClientState *nc, const uint8_t *buf,
     crc = cpu_to_be32(crc32(~0, buf, size));
     crc_ptr = (uint8_t *) &crc;
 
+    if (shift16) {
+        size += 2;
+    }
+
     /* Huge frames are truncted.  */
     if (size > s->regs[ENET_FTRL]) {
         size = s->regs[ENET_FTRL];
@@ -1087,6 +1092,24 @@ static ssize_t imx_enet_receive(NetClientState *nc, const uint8_t *buf,
             buf_len += size - 4;
         }
         buf_addr = bd.data;
+
+        if (shift16) {
+            /*
+             * If SHIFT16 bit of ENETx_RACC register is set we need to
+             * align the payload to 4-byte boundary.
+             */
+            const uint8_t zeros[2] = { 0 };
+
+            dma_memory_write(&address_space_memory, buf_addr,
+                             zeros, sizeof(zeros));
+
+            buf_addr += sizeof(zeros);
+            buf_len  -= sizeof(zeros);
+
+            /* We only do this once per Ethernet frame */
+            shift16 = false;
+        }
+
         dma_memory_write(&address_space_memory, buf_addr, buf, buf_len);
         buf += buf_len;
         if (size < 4) {

include/hw/net/imx_fec.h

@@ -170,6 +170,8 @@
 #define ENET_TWFR_TFWR_LENGTH  (6)
 #define ENET_TWFR_STRFWD       (1 << 8)
 
+#define ENET_RACC_SHIFT16      BIT(7)
+
 /* Buffer Descriptor.  */
 typedef struct {
     uint16_t length;