drivers: ethernet: adin2111: fix generic spi frame reception

Fixes a bug that results in double RX buffer read from ADIN
when generic SPI protocol is used.

Actual frame size to be read must be RX_FSIZE - HEADER.
If we read less amount of bytes, then ADIN raises an IRQ or
signals via Pn_RX_RDY that there is another frame available, as
we fail to read the whole frame.

The fix for "Still some length to go 2" is still present, we drop
the CRC32 bytes from the frame prior allocation and network
stack pass.

Signed-off-by: Georgij Cernysiov <geo.cgv@gmail.com>

Author: GeorgeCGV

drivers/ethernet/eth_adin2111.c

@@ -557,8 +557,8 @@ static int adin2111_read_fifo(const struct device *dev, const uint16_t port_idx)
 
 	/* burst read must be in multiples of 4 */
 	padding_len = ((fsize % 4) == 0) ? 0U : (ROUND_UP(fsize, 4U) - fsize);
-	/* actual frame length is FSIZE - FRAME HEADER - CRC32 */
-	fsize_real = fsize - (ADIN2111_FRAME_HEADER_SIZE + sizeof(uint32_t));
+	/* actual available frame length is FSIZE - FRAME HEADER */
+	fsize -= ADIN2111_FRAME_HEADER_SIZE;
 
 	/* spi header */
 	*(uint16_t *)cmd_buf = htons((ADIN2111_READ_TXN_CTRL | rx_reg));
@@ -574,7 +574,7 @@ static int adin2111_read_fifo(const struct device *dev, const uint16_t port_idx)
 	const struct spi_buf tx_buf = { .buf = cmd_buf, .len = sizeof(cmd_buf) };
 	const struct spi_buf rx_buf[3] = {
 		{.buf = NULL, .len = sizeof(cmd_buf) + ADIN2111_FRAME_HEADER_SIZE},
-		{.buf = ctx->buf, .len = fsize_real},
+		{.buf = ctx->buf, .len = fsize},
 		{.buf = NULL, .len = padding_len }
 	};
 	const struct spi_buf_set tx = { .buffers = &tx_buf, .count = 1U };
@@ -590,6 +590,9 @@ static int adin2111_read_fifo(const struct device *dev, const uint16_t port_idx)
 		return ret;
 	}
 
+	/* remove CRC32 and pass to the stack */
+	fsize_real = fsize - sizeof(uint32_t);
+
 	pkt = net_pkt_rx_alloc_with_buffer(iface, fsize_real, AF_UNSPEC, 0,
 					   K_MSEC(CONFIG_ETH_ADIN2111_TIMEOUT));
 	if (!pkt) {