net: smmac: allow configuring lower pbl values

The driver currently always sets the PBLx8/PBLx4 bit, which means that
the pbl values configured via the pbl/txpbl/rxpbl DT properties are
always multiplied by 8/4 in the hardware.

In order to allow the DT to configure lower pbl values, while at the
same time not changing behavior of any existing device trees using the
pbl/txpbl/rxpbl settings, add a property to disable the multiplication
of the pbl by 8/4 in the hardware.

Suggested-by: Rabin Vincent <rabinv@axis.com>
Signed-off-by: Niklas Cassel <niklas.cassel@axis.com>
Acked-by: Alexandre Torgue <alexandre.torgue@st.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/drivers/net/ethernet/stmicro/stmmac/dwmac4_dma.c b/drivers/net/ethernet/stmicro/stmmac/dwmac4_dma.c
index 2c3b209..8196ab5 100644
--- a/drivers/net/ethernet/stmicro/stmmac/dwmac4_dma.c
+++ b/drivers/net/ethernet/stmicro/stmmac/dwmac4_dma.c
@@ -84,7 +84,8 @@ static void dwmac4_dma_init_channel(void __iomem *ioaddr,
 	 * on each channel
 	 */
 	value = readl(ioaddr + DMA_CHAN_CONTROL(channel));
-	value = value | DMA_BUS_MODE_PBL;
+	if (dma_cfg->pblx8)
+		value = value | DMA_BUS_MODE_PBL;
 	writel(value, ioaddr + DMA_CHAN_CONTROL(channel));
 
 	value = readl(ioaddr + DMA_CHAN_TX_CONTROL(channel));