[PATCH RFC v2 08/11] net: stmmac: dwmac-meson8b: add support for the RX delay configuration

Martin Blumenstingl
2020-04-29T20:17:29Z

Configure the PRG_ETH0_ADJ_* bits to enable or disable the RX delay
based on the various RGMII PHY modes. For now the only supported RX
delay settings are:
- disabled, use for example for phy-mode "rgmii-id"
- 0ns - this is treated identical to "disabled", used for example on
boards where the PHY provides 2ns TX delay and the PCB trace length
already adds 2ns RX delay
- 2ns - for whenever the PHY cannot add the RX delay and the traces on
the PCB don't add any RX delay

Disabling the RX delay (in case u-boot enables it, which is the case
for example on Meson8b Odroid-C1) simply means that PRG_ETH0_ADJ_ENABLE,
PRG_ETH0_ADJ_SETUP, PRG_ETH0_ADJ_DELAY and PRG_ETH0_ADJ_SKEW should be
disabled (just disabling PRG_ETH0_ADJ_ENABLE may be enough, since that
disables the whole re-timing logic - but I find it makes more sense to
clear the other bits as well since they depend on that setting).

u-boot on Odroid-C1 uses the following steps to enable a 2ns RX delay:
- enabling enabling the timing adjustment clock
- enabling the timing adjustment logic by setting PRG_ETH0_ADJ_ENABLE
- setting the PRG_ETH0_ADJ_SETUP bit

The documentation for the PRG_ETH0_ADJ_DELAY and PRG_ETH0_ADJ_SKEW
registers indicates that we can even set different RX delays. However,
I could not find out how this works exactly, so for now we only support
a 2ns RX delay using the exact same way that Odroid-C1's u-boot does.

Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
---
.../ethernet/stmicro/stmmac/dwmac-meson8b.c | 79 +++++++++++++------
1 file changed, 56 insertions(+), 23 deletions(-)

diff --git a/drivers/net/ethernet/stmicro/stmmac/dwmac-meson8b.c b/drivers/net/ethernet/stmicro/stmmac/dwmac-meson8b.c
index d31f79c455de..73c84108d65b 100644
--- a/drivers/net/ethernet/stmicro/stmmac/dwmac-meson8b.c
+++ b/drivers/net/ethernet/stmicro/stmmac/dwmac-meson8b.c
@@ -85,6 +85,7 @@ struct meson8b_dwmac {
phy_interface_t phy_mode;
struct clk *rgmii_tx_clk;
u32 tx_delay_ns;
+ u32 rx_delay_ns;
struct clk *timing_adj_clk;
};

@@ -284,25 +285,58 @@ static int meson8b_devm_clk_prepare_enable(struct meson8b_dwmac *dwmac,

static int meson8b_init_prg_eth(struct meson8b_dwmac *dwmac)
{
+ u32 tx_dly_config, rx_dly_config, delay_config;
int ret;
- u8 tx_dly_val = 0;
+
+ tx_dly_config = FIELD_PREP(PRG_ETH0_TXDLY_MASK,
+ dwmac->tx_delay_ns >> 1);
+
+ if (dwmac->rx_delay_ns == 2)
+ rx_dly_config = PRG_ETH0_ADJ_ENABLE | PRG_ETH0_ADJ_SETUP;
+ else
+ rx_dly_config = 0;

switch (dwmac->phy_mode) {
case PHY_INTERFACE_MODE_RGMII:
+ delay_config = tx_dly_config | rx_dly_config;
+ break;
case PHY_INTERFACE_MODE_RGMII_RXID:
- tx_dly_val = dwmac->tx_delay_ns >> 1;
- /* fall through */
-
- case PHY_INTERFACE_MODE_RGMII_ID:
+ delay_config = tx_dly_config;
+ break;
case PHY_INTERFACE_MODE_RGMII_TXID:
+ delay_config = rx_dly_config;
+ break;
+ case PHY_INTERFACE_MODE_RGMII_ID:
+ case PHY_INTERFACE_MODE_RMII:
+ delay_config = 0;
+ break;
+ default:
+ dev_err(dwmac->dev, "unsupported phy-mode %s\n",
+ phy_modes(dwmac->phy_mode));
+ return -EINVAL;
+ };
+
+ if (rx_dly_config & PRG_ETH0_ADJ_ENABLE) {
+ /* The timing adjustment logic is driven by a separate clock */
+ ret = meson8b_devm_clk_prepare_enable(dwmac,
+ dwmac->timing_adj_clk);
+ if (ret) {
+ dev_err(dwmac->dev,
+ "Failed to enable the timing-adjustment clock\n");
+ return ret;
+ }
+ }
+
+ meson8b_dwmac_mask_bits(dwmac, PRG_ETH0, PRG_ETH0_TXDLY_MASK |
+ PRG_ETH0_ADJ_ENABLE | PRG_ETH0_ADJ_SETUP |
+ PRG_ETH0_ADJ_DELAY | PRG_ETH0_ADJ_SKEW,
+ delay_config);
+
+ if (phy_interface_mode_is_rgmii(dwmac->phy_mode)) {
/* only relevant for RMII mode -> disable in RGMII mode */
meson8b_dwmac_mask_bits(dwmac, PRG_ETH0,
PRG_ETH0_INVERTED_RMII_CLK, 0);

- meson8b_dwmac_mask_bits(dwmac, PRG_ETH0, PRG_ETH0_TXDLY_MASK,
- FIELD_PREP(PRG_ETH0_TXDLY_MASK,
- tx_dly_val));
-
/* Configure the 125MHz RGMII TX clock, the IP block changes
* the output automatically (= without us having to configure
* a register) based on the line-speed (125MHz for Gbit speeds,
@@ -322,24 +356,11 @@ static int meson8b_init_prg_eth(struct meson8b_dwmac *dwmac)
"failed to enable the RGMII TX clock\n");
return ret;
}
- break;
-
- case PHY_INTERFACE_MODE_RMII:
+ } else {
/* 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->dev, "unsupported phy-mode %s\n",
- phy_modes(dwmac->phy_mode));
- return -EINVAL;
}

/* enable TX_CLK and PHY_REF_CLK generator */
@@ -394,6 +415,18 @@ static int meson8b_dwmac_probe(struct platform_device *pdev)
&dwmac->tx_delay_ns))
dwmac->tx_delay_ns = 2;

+ /* use 0ns as fallback since this is what most boards actually use */
+ if (of_property_read_u32(pdev->dev.of_node, "amlogic,rx-delay-ns",
+ &dwmac->rx_delay_ns))
+ dwmac->rx_delay_ns = 0;
+
+ if (dwmac->rx_delay_ns != 0 && dwmac->rx_delay_ns != 2) {
+ dev_err(&pdev->dev,
+ "The only allowed RX delays values are: 0ns, 2ns");
+ ret = -EINVAL;
+ goto err_remove_config_dt;
+ }
+
dwmac->timing_adj_clk = devm_clk_get_optional(dwmac->dev,
"timing-adjustment");
if (IS_ERR(dwmac->timing_adj_clk)) {
--
2.26.2