Re: [PATCH net-next v3 3/3] net: stmmac: Add glue layer for Spacemit K3 SoC

[Vivian Wang <wangruikang@iscas.ac.cn>]

Hi Inochi,

I have some comments below.

On 1/28/26 15:29, Inochi Amaoto wrote:
> The etherenet controller on Spacemit K3 SoC is Synopsys DesignWare
Typo: etherenet -> ethernet
> MAC (version 5.40a), with the following special point:
Nit: point -> points 
> 1. The rate of the tx clock line is auto changed when the mac speed
>    rate is changed, and no need for changing the input tx clock.
> 2. This controller require a extra syscon device to configure the
>    interface type, enable wake up interrupt and delay configuration
>    if needed.
>
> Add Spacemit dwmac driver support on the Spacemit K3 SoC.
>
> Signed-off-by: Inochi Amaoto <inochiama@gmail.com>
> ---
>  drivers/net/ethernet/stmicro/stmmac/Kconfig   |  12 +
>  drivers/net/ethernet/stmicro/stmmac/Makefile  |   1 +
>  .../ethernet/stmicro/stmmac/dwmac-spacemit.c  | 218 ++++++++++++++++++
>  3 files changed, 231 insertions(+)
>  create mode 100644 drivers/net/ethernet/stmicro/stmmac/dwmac-spacemit.c
>
> [...]
>
> +
> +/* dline register bits */
> +#define RGMII_RX_DLINE_EN		BIT(0)
> +#define RGMII_RX_DLINE_STEP		GENMASK(5, 4)
> +#define RGMII_RX_DLINE_CODE		GENMASK(15, 8)
> +#define RGMII_TX_DLINE_EN		BIT(16)
> +#define RGMII_TX_DLINE_STEP		GENMASK(21, 20)
> +#define RGMII_TX_DLINE_CODE		GENMASK(31, 24)
> +
> +#define MAX_DLINE_DELAY_CODE		0xff
> +#define MAX_WORKED_DELAY		2800
> +
> +/* Note: the delay step value is at 0.1ps */
> +static const unsigned int k3_delay_step_10x[4] = {
> +	367, 493, 559, 685
> +};
> +
> +static int spacemit_dwmac_set_delay(struct regmap *apmu,
> +				    unsigned int dline_offset,
> +				    unsigned int tx_code, unsigned int tx_config,
> +				    unsigned int rx_code, unsigned int rx_config)
> +{
> +	unsigned int mask, val;
> +
> +	mask = RGMII_TX_DLINE_STEP | RGMII_TX_DLINE_CODE | RGMII_TX_DLINE_EN |
> +	       RGMII_RX_DLINE_STEP | RGMII_RX_DLINE_CODE | RGMII_RX_DLINE_EN;
> +	val = FIELD_PREP(RGMII_TX_DLINE_STEP, tx_config) |
> +	      FIELD_PREP(RGMII_TX_DLINE_CODE, tx_code) | RGMII_TX_DLINE_EN |
> +	      FIELD_PREP(RGMII_RX_DLINE_STEP, rx_config) |
> +	      FIELD_PREP(RGMII_RX_DLINE_CODE, rx_code) | RGMII_RX_DLINE_EN;
> +
> +	return regmap_update_bits(apmu, dline_offset, mask, val);
> +}
> +
> +static int spacemit_dwmac_detected_delay_value(unsigned int delay,
> +					       unsigned int *config)
> +{
> +	unsigned int best_delay = 0;
> +	unsigned int best_config = 0;
> +	int best_code = 0;
> +	int i;
> +
> +	if (delay == 0)
> +		return 0;
> +
> +	if (delay > MAX_WORKED_DELAY)
> +		return -EINVAL;
> +
> +	/*
> +	 * Note K3 require a specific factor for calculate
> +	 * the delay, in this scenario it is 0.9. So the
> +	 * formula is code * step / 10 * 0.9
> +	 */
> +	for (i = 0; i < ARRAY_SIZE(k3_delay_step_10x); i++) {
> +		unsigned int step = k3_delay_step_10x[i];
> +		int code = DIV_ROUND_CLOSEST(delay * 10 * 10, step * 9);
> +		unsigned int tmp = code * step * 9 / 10 / 10;
> +
> +		if (abs(tmp - delay) < abs(best_delay - delay)) {
> +			best_code = code;
> +			best_delay = tmp;
> +			best_config = i;
> +		}
> +	}
> +
> +	*config = best_config;
> +
> +	return best_code;

Is this really necessary? For K1 I just used the smallest step size.

It seems to me you have, for the smallest step size, about 36.7ps * 0.9
= 33ps per step. Theoretically speaking that lets you fine tune the
delay to within 1% of the 2ns total required RGMII delay (MAC + PCB +
PHY). In practice this number shouldn't be that marginal.