ravb: Add rx_max_buf_size to struct ravb_hw_info

R-Car AVB-DMAC has maximum 2K size on RX buffer, whereas on RZ/G2L
it is 8K. We need to allow for changing the MTU within the limit
of the maximum size of a descriptor.

Add a rx_max_buf_size variable to struct ravb_hw_info to handle
this difference.
Signed-off-by: Biju Das <biju.das.jz@bp.renesas.com>
Reviewed-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Reviewed-by: Sergey Shtylyov <s.shtylyov@omp.ru>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/ethernet/renesas/ravb.h

@@ -1010,6 +1010,7 @@ struct ravb_hw_info {
 	int stats_len;
 	size_t max_rx_len;
 	u32 tsrq;
+	u32 rx_max_buf_size;
 	unsigned aligned_tx: 1;
 
 	/* hardware features */

drivers/net/ethernet/renesas/ravb_main.c

@@ -2188,6 +2188,7 @@ static const struct ravb_hw_info ravb_gen3_hw_info = {
 	.stats_len = ARRAY_SIZE(ravb_gstrings_stats),
 	.max_rx_len = RX_BUF_SZ + RAVB_ALIGN - 1,
 	.tsrq = TCCR_TSRQ0 | TCCR_TSRQ1 | TCCR_TSRQ2 | TCCR_TSRQ3,
+	.rx_max_buf_size = SZ_2K,
 	.internal_delay = 1,
 	.tx_counters = 1,
 	.multi_irqs = 1,
@@ -2212,6 +2213,7 @@ static const struct ravb_hw_info ravb_gen2_hw_info = {
 	.stats_len = ARRAY_SIZE(ravb_gstrings_stats),
 	.max_rx_len = RX_BUF_SZ + RAVB_ALIGN - 1,
 	.tsrq = TCCR_TSRQ0 | TCCR_TSRQ1 | TCCR_TSRQ2 | TCCR_TSRQ3,
+	.rx_max_buf_size = SZ_2K,
 	.aligned_tx = 1,
 	.gptp = 1,
 	.nc_queue = 1,
@@ -2229,6 +2231,7 @@ static const struct ravb_hw_info gbeth_hw_info = {
 	.emac_init = ravb_emac_init_gbeth,
 	.max_rx_len = ALIGN(GBETH_RX_BUFF_MAX, RAVB_ALIGN),
 	.tsrq = TCCR_TSRQ0,
+	.rx_max_buf_size = SZ_8K,
 	.aligned_tx = 1,
 	.tx_counters = 1,
 	.half_duplex = 1,
@@ -2452,7 +2455,7 @@ static int ravb_probe(struct platform_device *pdev)
 	}
 	clk_prepare_enable(priv->refclk);
 
-	ndev->max_mtu = 2048 - (ETH_HLEN + VLAN_HLEN + ETH_FCS_LEN);
+	ndev->max_mtu = info->rx_max_buf_size - (ETH_HLEN + VLAN_HLEN + ETH_FCS_LEN);
 	ndev->min_mtu = ETH_MIN_MTU;
 
 	/* FIXME: R-Car Gen2 has 4byte alignment restriction for tx buffer