bcmgenet: fix Rx buffer corruption caused by lack of cache flush

When bcmgenet complete to write Rx buffer with the DMA,
some U-Boot commands write data to the buffer directly.
Those write data will become dirty in CPU cache.
After this driver calls free_pkt to the buffer,
the buffer is assigned as the future Rx buffer.
At some point, if bcmgenet writes to a buffer with DMA
and CPU cache flushes dirty data to the buffer,
the buffer is corrupted.

This patch calls flush_dcache_range in free_pkt
to immediately flush the data written by U-Boot command
and prevent data corruption.

This issue can be reproduced using wget on Raspberry Pi4.
If wget receives data larger than
RX_BUF_LENGTH * RX_DESCS = 2048 * 256 bytes,
it will timeout due to data corruption.
In addition, if LOG_DEBUG is enabled in net/tcp.c,
the following error log is output.

TCP RX TCP xSum Error

Signed-off-by: Yasuharu Shibata <yasuharu.shibata@gmail.com>

drivers/net/bcmgenet.c

@@ -360,6 +360,10 @@ static int bcmgenet_gmac_free_pkt(struct udevice *dev, uchar *packet,
 				  int length)
 {
 	struct bcmgenet_eth_priv *priv = dev_get_priv(dev);
+	void *desc_base = priv->rx_desc_base + priv->rx_index * DMA_DESC_SIZE;
+	u32 addr = readl(desc_base + DMA_DESC_ADDRESS_LO);
+
+	flush_dcache_range(addr, addr + RX_BUF_LENGTH);
 
 	/* Tell the MAC we have consumed that last receive buffer. */
 	priv->c_index = (priv->c_index + 1) & 0xFFFF;