net: stmmac: Parse FIFO sizes from feature registers

New version of this core encode the FIFO sizes in one of the feature
registers. Use these sizes as default, but still allow device tree to
override them for backwards compatibility.
Reviewed-by: Mikko Perttunen <mperttunen@nvidia.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/stmicro/stmmac/common.h

@@ -324,6 +324,9 @@ struct dma_features {
 	unsigned int number_tx_queues;
 	/* Alternate (enhanced) DESC mode */
 	unsigned int enh_desc;
+	/* TX and RX FIFO sizes */
+	unsigned int tx_fifo_size;
+	unsigned int rx_fifo_size;
 };
 
 /* GMAC TX FIFO is 8K, Rx FIFO is 16K */

drivers/net/ethernet/stmicro/stmmac/dwmac4.h

@@ -148,6 +148,8 @@ enum power_event {
 /* MAC HW features1 bitmap */
 #define GMAC_HW_FEAT_AVSEL		BIT(20)
 #define GMAC_HW_TSOEN			BIT(18)
+#define GMAC_HW_TXFIFOSIZE		GENMASK(10, 6)
+#define GMAC_HW_RXFIFOSIZE		GENMASK(4, 0)
 
 /* MAC HW features2 bitmap */
 #define GMAC_HW_FEAT_TXCHCNT		GENMASK(21, 18)

drivers/net/ethernet/stmicro/stmmac/dwmac4_dma.c

@@ -294,6 +294,11 @@ static void dwmac4_get_hw_feature(void __iomem *ioaddr,
 	hw_cap = readl(ioaddr + GMAC_HW_FEATURE1);
 	dma_cap->av = (hw_cap & GMAC_HW_FEAT_AVSEL) >> 20;
 	dma_cap->tsoen = (hw_cap & GMAC_HW_TSOEN) >> 18;
+	/* RX and TX FIFO sizes are encoded as log2(n / 128). Undo that by
+	 * shifting and store the sizes in bytes.
+	 */
+	dma_cap->tx_fifo_size = 128 << ((hw_cap & GMAC_HW_TXFIFOSIZE) >> 6);
+	dma_cap->rx_fifo_size = 128 << ((hw_cap & GMAC_HW_RXFIFOSIZE) >> 0);
 	/* MAC HW feature2 */
 	hw_cap = readl(ioaddr + GMAC_HW_FEATURE2);
 	/* TX and RX number of channels */

drivers/net/ethernet/stmicro/stmmac/stmmac_main.c

@@ -1281,6 +1281,9 @@ static void stmmac_dma_operation_mode(struct stmmac_priv *priv)
 {
 	int rxfifosz = priv->plat->rx_fifo_size;
 
+	if (rxfifosz == 0)
+		rxfifosz = priv->dma_cap.rx_fifo_size;
+
 	if (priv->plat->force_thresh_dma_mode)
 		priv->hw->dma->dma_mode(priv->ioaddr, tc, tc, rxfifosz);
 	else if (priv->plat->force_sf_dma_mode || priv->plat->tx_coe) {