Re: [PATCH net-next] net: stmmac: dwmac-qcom-ethqos: Add support for 2.5G SGMII

[Maxime Chevallier <maxime.chevallier@bootlin.com>]

Hi,

On Mon, 18 Dec 2023 12:41:18 +0530
Sneh Shah <quic_snehshah@quicinc.com> wrote:

> Serdes phy needs to operate at 2500 mode for 2.5G speed and 1000
> mode for 1G/100M/10M speed.
> Added changes to configure serdes phy and mac based on link speed.
> 
> Signed-off-by: Sneh Shah <quic_snehshah@quicinc.com>
> ---
>  .../stmicro/stmmac/dwmac-qcom-ethqos.c        | 31 +++++++++++++++++--
>  1 file changed, 29 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/net/ethernet/stmicro/stmmac/dwmac-qcom-ethqos.c b/drivers/net/ethernet/stmicro/stmmac/dwmac-qcom-ethqos.c
> index d3bf42d0fceb..b3a28dc19161 100644
> --- a/drivers/net/ethernet/stmicro/stmmac/dwmac-qcom-ethqos.c
> +++ b/drivers/net/ethernet/stmicro/stmmac/dwmac-qcom-ethqos.c
> @@ -21,6 +21,7 @@
>  #define RGMII_IO_MACRO_CONFIG2		0x1C
>  #define RGMII_IO_MACRO_DEBUG1		0x20
>  #define EMAC_SYSTEM_LOW_POWER_DEBUG	0x28
> +#define ETHQOS_MAC_AN_CTRL		0xE0
>  
>  /* RGMII_IO_MACRO_CONFIG fields */
>  #define RGMII_CONFIG_FUNC_CLK_EN		BIT(30)
> @@ -78,6 +79,10 @@
>  #define ETHQOS_MAC_CTRL_SPEED_MODE		BIT(14)
>  #define ETHQOS_MAC_CTRL_PORT_SEL		BIT(15)
>  
> +/*ETHQOS_MAC_AN_CTRL bits */
> +#define ETHQOS_MAC_AN_CTRL_RAN			BIT(9)
> +#define ETHQOS_MAC_AN_CTRL_ANE			BIT(12)
> +
>  struct ethqos_emac_por {
>  	unsigned int offset;
>  	unsigned int value;
> @@ -109,6 +114,7 @@ struct qcom_ethqos {
>  	unsigned int num_por;
>  	bool rgmii_config_loopback_en;
>  	bool has_emac_ge_3;
> +	unsigned int serdes_speed;

Looks like you are storing SPEED_XXX definitions here, which can be
negative in case of SPEED_UNKNOWN, so this should be an int.

>  };
>  
>  static int rgmii_readl(struct qcom_ethqos *ethqos, unsigned int offset)
> @@ -600,27 +606,47 @@ static int ethqos_configure_rgmii(struct qcom_ethqos *ethqos)
>  
>  static int ethqos_configure_sgmii(struct qcom_ethqos *ethqos)
>  {
> -	int val;
> -
> +	int val, mac_an_value;
>  	val = readl(ethqos->mac_base + MAC_CTRL_REG);
> +	mac_an_value = readl(ethqos->mac_base + ETHQOS_MAC_AN_CTRL);
>  
>  	switch (ethqos->speed) {
> +	case SPEED_2500:
> +		val &= ~ETHQOS_MAC_CTRL_PORT_SEL;
> +		rgmii_updatel(ethqos, RGMII_CONFIG2_RGMII_CLK_SEL_CFG,
> +			      RGMII_CONFIG2_RGMII_CLK_SEL_CFG,
> +			      RGMII_IO_MACRO_CONFIG2);
> +		if (ethqos->serdes_speed != SPEED_2500)
> +			phy_set_speed(ethqos->serdes_phy, ethqos->speed);
> +		mac_an_value &= ~ETHQOS_MAC_AN_CTRL_ANE;
> +		break;
>  	case SPEED_1000:
>  		val &= ~ETHQOS_MAC_CTRL_PORT_SEL;
>  		rgmii_updatel(ethqos, RGMII_CONFIG2_RGMII_CLK_SEL_CFG,
>  			      RGMII_CONFIG2_RGMII_CLK_SEL_CFG,
>  			      RGMII_IO_MACRO_CONFIG2);
> +		if (ethqos->serdes_speed != SPEED_1000)
> +			phy_set_speed(ethqos->serdes_phy, ethqos->speed);
> +		mac_an_value |= ETHQOS_MAC_AN_CTRL_RAN | ETHQOS_MAC_AN_CTRL_ANE;
>  		break;
>  	case SPEED_100:
>  		val |= ETHQOS_MAC_CTRL_PORT_SEL | ETHQOS_MAC_CTRL_SPEED_MODE;
> +		if (ethqos->serdes_speed != SPEED_1000)
> +			phy_set_speed(ethqos->serdes_phy, ethqos->speed);

I understand that SGMII's serdes always runs at 1000 / 2500, but this
check doesn't make much sense then, if the speed isn't 1000, then you
set the serdes PHY's speed to 100, and the assignment that comes after
that switch-case will also set the serdes speed to 100.

Also, if the serdes PHY really needs to be configured differently for
10/100/1000, then switching from speed 1000 to speed 100 for example
won't trigger a serdes PHY reconfiguration here.

My guess is that you want something like :

	phy_set_speed(ethqos->serdes_phy, SPEED_1000)

and the assignment at the end of the switch-case should be
SPEED_1000/SPEED_2500 only (see the comment bellow).

> +		mac_an_value |= ETHQOS_MAC_AN_CTRL_RAN | ETHQOS_MAC_AN_CTRL_ANE;
>  		break;
>  	case SPEED_10:
>  		val |= ETHQOS_MAC_CTRL_PORT_SEL;
>  		val &= ~ETHQOS_MAC_CTRL_SPEED_MODE;
> +		if (ethqos->serdes_speed != SPEED_1000)
> +			phy_set_speed(ethqos->serdes_phy, ethqos->speed);

Same remark here

> +		mac_an_value |= ETHQOS_MAC_AN_CTRL_RAN | ETHQOS_MAC_AN_CTRL_ANE;
>  		break;
>  	}
>  
>  	writel(val, ethqos->mac_base + MAC_CTRL_REG);
> +	writel(mac_an_value, ethqos->mac_base + ETHQOS_MAC_AN_CTRL);
> +	ethqos->serdes_speed = ethqos->speed;

Although the code will behave the same, as you are storing the true
serdes speed here, shouldn't it be either SPEED_1000 or SPEED_2500 ?

You'll end-up storing SPEED_10 / SPEED_100 should the link use these
speeds, which doesn't represent the true serdes speed.

This would spare serdes reconfigurations when alternating between
10/100/1000M speeds.

>  	return val;
>  }
> @@ -789,6 +815,7 @@ static int qcom_ethqos_probe(struct platform_device *pdev)
>  				     "Failed to get serdes phy\n");
>  
>  	ethqos->speed = SPEED_1000;
> +	ethqos->serdes_speed = SPEED_1000;
>  	ethqos_update_link_clk(ethqos, SPEED_1000);
>  	ethqos_set_func_clk_en(ethqos);
>  

Thanks,

Maxime