Martin Blumenstingl [off-list ref] writes:

The Ethernet controller available in Meson8b and GXBB SoCs is a Synopsys
DesignWare MAC IP core which is already supported by the stmmac driver.

In addition to the standard stmmac driver some Meson8b / GXBB specific
registers have to be configured for the PHY clocks. These SoC specific
registers are called PRG_ETHERNET_ADDR0 and PRG_ETHERNET_ADDR1 in the
datasheet.
These registers are not backwards compatible with those on Meson 6b,
which is why a new glue driver is introduced. This worked for many
boards because the bootloader programs the PRG_ETHERNET registers
correctly. Additionally the meson6-dwmac driver only sets bit 1 of
PRG_ETHERNET_ADDR0 which (according to the datasheet) is only used
during reset.

Currently all configuration values can be determined automatically,
based on the configured phy-mode (which is mandatory for the stmmac
driver). If required the tx-delay and the mux clock (so it supports
the MPLL2 clock as well) can be made configurable in the future.

Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>

[...]

+static int meson8b_init_clk(struct meson8b_dwmac *dwmac)
+{
+	struct clk_init_data init;
+	int i, ret;
+	struct device *dev = &dwmac->pdev->dev;
+	char clk_name[32];
+	const char *clk_div_parents[1];
+	const char *mux_parent_names[MUX_CLK_NUM_PARENTS];
+	unsigned int mux_parent_count = 0;
+	static struct clk_div_table clk_25m_div_table[] = {
+		{ .val = 0, .div = 5 },
+		{ .val = 1, .div = 10 },
+		{ /* sentinel */ },
+	};
+
+	/* get the mux parents from DT */
+	for (i = 0; i < MUX_CLK_NUM_PARENTS; i++) {
+		char name[16];
+
+		snprintf(name, sizeof(name), "clkin%d", i);
+		dwmac->m250_mux_parent[i] = devm_clk_get(dev, name);
+		if (IS_ERR(dwmac->m250_mux_parent[i])) {
+			/* NOTE: the second clock (MP2) is unused on all known

nit: multi-line comment style  (c.f. Documentation/CodingStyle search
for "multi-line")

+			 * boards, thus we're making it optional here.
+			 */
+			if (i > 0)
+				continue;

IMO, this is a bit confusing.  I think this should either be coded to
deal with an optional "clkin1" (preferred), or it should be coded to
without a mux and clkin0 is directly the parent of the divider.  The
current way of always bailing out of this loop early is a bit confusing.

+			ret = PTR_ERR(dwmac->m250_mux_parent[i]);
+			if (ret != -EPROBE_DEFER)
+				dev_err(dev, "Missing clock %s\n", name);
+			dwmac->m250_mux_parent[i] = NULL;
+			return ret;
+		}
+
+		mux_parent_names[i] =
+			__clk_get_name(dwmac->m250_mux_parent[i]);
+		mux_parent_count++;
+	}
+
+	/* create the m250_mux */
+	snprintf(clk_name, sizeof(clk_name), "%s#m250_sel", dev_name(dev));
+	init.name = clk_name;
+	init.ops = &clk_mux_ops;
+	init.flags = CLK_IS_BASIC;
+	init.parent_names = mux_parent_names;
+	init.num_parents = mux_parent_count;
+
+	dwmac->m250_mux.reg = dwmac->regs + PRG_ETH0;
+	dwmac->m250_mux.shift = PRG_ETH0_CLK_M250_SEL_SHIFT;
+	dwmac->m250_mux.mask = PRG_ETH0_CLK_M250_SEL_MASK;
+	dwmac->m250_mux.flags = 0;
+	dwmac->m250_mux.table = NULL;
+	dwmac->m250_mux.hw.init = &init;
+
+	dwmac->m250_mux_clk = devm_clk_register(dev, &dwmac->m250_mux.hw);
+	if (WARN_ON(PTR_ERR_OR_ZERO(dwmac->m250_mux_clk)))
+		return PTR_ERR(dwmac->m250_mux_clk);
+
+	/* create the m250_div */
+	snprintf(clk_name, sizeof(clk_name), "%s#m250_div", dev_name(dev));
+	init.name = devm_kstrdup(dev, clk_name, GFP_KERNEL);
+	init.ops = &clk_divider_ops;
+	init.flags = CLK_IS_BASIC | CLK_SET_RATE_PARENT;

hmm, with CLK_SET_RATE_PARENT that implies that it might switch the mux,
but it's hard-coded above so the mux only ever has one parent, so that
can never happen.

+	clk_div_parents[0] = __clk_get_name(dwmac->m250_mux_clk);
+	init.parent_names = clk_div_parents;
+	init.num_parents = ARRAY_SIZE(clk_div_parents);
+
+	dwmac->m250_div.reg = dwmac->regs + PRG_ETH0;
+	dwmac->m250_div.shift = PRG_ETH0_CLK_M250_DIV_SHIFT;
+	dwmac->m250_div.width = PRG_ETH0_CLK_M250_DIV_WIDTH;
+	dwmac->m250_div.hw.init = &init;
+	dwmac->m250_div.flags = CLK_DIVIDER_ONE_BASED | CLK_DIVIDER_ALLOW_ZERO;
+
+	dwmac->m250_div_clk = devm_clk_register(dev, &dwmac->m250_div.hw);
+	if (WARN_ON(PTR_ERR_OR_ZERO(dwmac->m250_div_clk)))
+		return PTR_ERR(dwmac->m250_div_clk);
+
+	/* create the m25_div */
+	snprintf(clk_name, sizeof(clk_name), "%s#m25_div", dev_name(dev));
+	init.name = devm_kstrdup(dev, clk_name, GFP_KERNEL);
+	init.ops = &clk_divider_ops;
+	init.flags = CLK_IS_BASIC | CLK_SET_RATE_PARENT;
+	clk_div_parents[0] = __clk_get_name(dwmac->m250_div_clk);
+	init.parent_names = clk_div_parents;
+	init.num_parents = ARRAY_SIZE(clk_div_parents);
+
+	dwmac->m25_div.reg = dwmac->regs + PRG_ETH0;
+	dwmac->m25_div.shift = PRG_ETH0_CLK_M25_DIV_SHIFT;
+	dwmac->m25_div.width = PRG_ETH0_CLK_M25_DIV_WIDTH;
+	dwmac->m25_div.table = clk_25m_div_table;
+	dwmac->m25_div.hw.init = &init;
+	dwmac->m25_div.flags = CLK_DIVIDER_ALLOW_ZERO;
+
+	dwmac->m25_div_clk = devm_clk_register(dev, &dwmac->m25_div.hw);
+	if (WARN_ON(PTR_ERR_OR_ZERO(dwmac->m25_div_clk)))
+		return PTR_ERR(dwmac->m25_div_clk);
+
+	return 0;
+}
+
+static int meson8b_init_prg_eth(struct meson8b_dwmac *dwmac)
+{
+	int ret;
+	unsigned long clk_rate;
+
+	switch (dwmac->phy_mode) {
+	case PHY_INTERFACE_MODE_RGMII:
+	case PHY_INTERFACE_MODE_RGMII_ID:
+	case PHY_INTERFACE_MODE_RGMII_RXID:
+	case PHY_INTERFACE_MODE_RGMII_TXID:
+		/* Generate a 25MHz clock for the PHY */
+		clk_rate = 25 * 1000 * 1000;
+
+		/* enable RGMII mode */
+		meson8b_dwmac_mask_bits(dwmac, PRG_ETH0, PRG_ETH0_RGMII_MODE,
+					PRG_ETH0_RGMII_MODE);
+
+		/* only relevant for RMII mode -> disable in RGMII mode */
+		meson8b_dwmac_mask_bits(dwmac, PRG_ETH0,
+					PRG_ETH0_INVERTED_RMII_CLK, 0);
+
+		/* TX clock delay - all known boards use a 1/4 cycle delay */
+		meson8b_dwmac_mask_bits(dwmac, PRG_ETH0, PRG_ETH0_TXDLY_MASK,
+					PRG_ETH0_TXDLY_QUARTER);
+		break;
+
+	case PHY_INTERFACE_MODE_RMII:
+		/* Use the rate of the mux clock for the internal RMII PHY */
+		clk_rate = clk_get_rate(dwmac->m250_mux_clk);
+
+		/* disable RGMII mode -> enables RMII mode */
+		meson8b_dwmac_mask_bits(dwmac, PRG_ETH0, PRG_ETH0_RGMII_MODE,
+					0);
+
+		/* invert internal clk_rmii_i to generate 25/2.5 tx_rx_clk */
+		meson8b_dwmac_mask_bits(dwmac, PRG_ETH0,
+					PRG_ETH0_INVERTED_RMII_CLK,
+					PRG_ETH0_INVERTED_RMII_CLK);
+
+		/* TX clock delay cannot be configured in RMII mode */
+		meson8b_dwmac_mask_bits(dwmac, PRG_ETH0, PRG_ETH0_TXDLY_MASK,
+					0);
+
+		break;
+
+	default:
+		dev_err(&dwmac->pdev->dev, "unsupported phy-mode %s\n",
+			phy_modes(dwmac->phy_mode));
+		return -EINVAL;
+	}
+
+	ret = clk_prepare_enable(dwmac->m25_div_clk);
+	if (ret) {
+		dev_err(&dwmac->pdev->dev, "failed to enable the PHY clock\n");
+		return ret;
+	}
+
+	ret = clk_set_rate(dwmac->m25_div_clk, clk_rate);
+	if (ret) {
+		clk_disable_unprepare(dwmac->m25_div_clk);
+
+		dev_err(&dwmac->pdev->dev, "failed to set PHY clock\n");
+		return ret;
+	}

In the case of success, the clock is never disabled/unprepared.   You
probably need a .remove function which disables the clock and then calls
stmmac_pltfr_remove.

+	/* enable TX_CLK and PHY_REF_CLK generator */
+	meson8b_dwmac_mask_bits(dwmac, PRG_ETH0, PRG_ETH0_TX_AND_PHY_REF_CLK,
+				PRG_ETH0_TX_AND_PHY_REF_CLK);
+
+	return 0;
+}

[...]

Otherwise, this is looking good.

Also, I tested on meson-gxbb-odroidc2 and meson-gxbb-p200 by booting a debian
root filesystem over NFS and all was well.

Tested-by: Kevin Hilman <khilman@baylibre.com>

Kevin