Re: [PATCH] phy: ti: gmii-sel: Force RGMII TX delay

[Matthias Schiffer <matthias.schiffer@ew.tq-group.com>]

On Mon, 2025-08-04 at 16:06 +0200, Michael Walle wrote:
> Some SoCs are just validated with the TX delay enabled. With commit
> ca13b249f291 ("net: ethernet: ti: am65-cpsw: fixup PHY mode for fixed
> RGMII TX delay"), the network driver will patch the delay setting on the
> fly assuming that the TX delay is fixed. In reality, the TX delay is
> configurable and just skipped in the documentation. There are
> bootloaders, which will disable the TX delay and this will lead to a
> transmit path which doesn't add any delays at all. Fix that by always
> forcing the TX delay to be enabled.
> 
> Fixes: ca13b249f291 ("net: ethernet: ti: am65-cpsw: fixup PHY mode for fixed RGMII TX delay")
> Signed-off-by: Michael Walle <mwalle@kernel.org>
> ---
>  drivers/phy/ti/phy-gmii-sel.c | 52 +++++++++++++++++++++++++++++------
>  1 file changed, 44 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/phy/ti/phy-gmii-sel.c b/drivers/phy/ti/phy-gmii-sel.c
> index ff5d5e29629f..a0c19d00ff3a 100644
> --- a/drivers/phy/ti/phy-gmii-sel.c
> +++ b/drivers/phy/ti/phy-gmii-sel.c
> @@ -34,6 +34,7 @@ enum {
>  	PHY_GMII_SEL_PORT_MODE = 0,
>  	PHY_GMII_SEL_RGMII_ID_MODE,
>  	PHY_GMII_SEL_RMII_IO_CLK_EN,
> +	PHY_GMII_SEL_FIXED_TX_DELAY,
>  	PHY_GMII_SEL_LAST,
>  };
>  
> @@ -127,6 +128,16 @@ static int phy_gmii_sel_mode(struct phy *phy, enum phy_mode mode, int submode)
>  		goto unsupported;
>  	}
>  
> +	/*
> +	 * Some SoCs only support fixed MAC side TX delays. According to the
> +	 * datasheet, they are always enabled, but that turns out not to be the
> +	 * case and the delay is configurable. But according to the vendor that
> +	 * mode is not validated and might not work. Some bootloaders disable
> +	 * that bit. To work around that enable it again.
> +	 */
> +	if (soc_data->features & BIT(PHY_GMII_SEL_FIXED_TX_DELAY))
> +		rgmii_id = 0;

The mode passed to phy_gmii_sel_mode by am65-cpsw is the same value that is
passed to the Ethernet PHY driver, so a case where rgmii_id == 1 and would be
reset to 0 is unreachable (PHY_INTERFACE_MODE_RGMII_ID and
PHY_INTERFACE_MODE_RGMII_TXID can't occur with the fixup in am65-cpsw).
Therefore we could return EINVAL here if PHY_GMII_SEL_FIXED_TX_DELAY is set and
rgmii_id == 1 instead of effectively ignoring the mode, which seems a bit more
robust to me.

Best,
Matthias


> +
>  	if_phy->phy_if_mode = submode;
>  
>  	dev_dbg(dev, "%s id:%u mode:%u rgmii_id:%d rmii_clk_ext:%d\n",
> @@ -210,25 +221,46 @@ struct phy_gmii_sel_soc_data phy_gmii_sel_soc_dm814 = {
>  
>  static const
>  struct reg_field phy_gmii_sel_fields_am654[][PHY_GMII_SEL_LAST] = {
> -	{ [PHY_GMII_SEL_PORT_MODE] = REG_FIELD(0x0, 0, 2), },
> -	{ [PHY_GMII_SEL_PORT_MODE] = REG_FIELD(0x4, 0, 2), },
> -	{ [PHY_GMII_SEL_PORT_MODE] = REG_FIELD(0x8, 0, 2), },
> -	{ [PHY_GMII_SEL_PORT_MODE] = REG_FIELD(0xC, 0, 2), },
> -	{ [PHY_GMII_SEL_PORT_MODE] = REG_FIELD(0x10, 0, 2), },
> -	{ [PHY_GMII_SEL_PORT_MODE] = REG_FIELD(0x14, 0, 2), },
> -	{ [PHY_GMII_SEL_PORT_MODE] = REG_FIELD(0x18, 0, 2), },
> -	{ [PHY_GMII_SEL_PORT_MODE] = REG_FIELD(0x1C, 0, 2), },
> +	{
> +		[PHY_GMII_SEL_PORT_MODE] = REG_FIELD(0x0, 0, 2),
> +		[PHY_GMII_SEL_RGMII_ID_MODE] = REG_FIELD(0x0, 4, 4),
> +	}, {
> +		[PHY_GMII_SEL_PORT_MODE] = REG_FIELD(0x4, 0, 2),
> +		[PHY_GMII_SEL_RGMII_ID_MODE] = REG_FIELD(0x4, 4, 4),
> +	}, {
> +		[PHY_GMII_SEL_PORT_MODE] = REG_FIELD(0x8, 0, 2),
> +		[PHY_GMII_SEL_RGMII_ID_MODE] = REG_FIELD(0x8, 4, 4),
> +	}, {
> +		[PHY_GMII_SEL_PORT_MODE] = REG_FIELD(0xC, 0, 2),
> +		[PHY_GMII_SEL_RGMII_ID_MODE] = REG_FIELD(0xC, 4, 4),
> +	}, {
> +		[PHY_GMII_SEL_PORT_MODE] = REG_FIELD(0x10, 0, 2),
> +		[PHY_GMII_SEL_RGMII_ID_MODE] = REG_FIELD(0x10, 4, 4),
> +	}, {
> +		[PHY_GMII_SEL_PORT_MODE] = REG_FIELD(0x14, 0, 2),
> +		[PHY_GMII_SEL_RGMII_ID_MODE] = REG_FIELD(0x14, 4, 4),
> +	}, {
> +		[PHY_GMII_SEL_PORT_MODE] = REG_FIELD(0x18, 0, 2),
> +		[PHY_GMII_SEL_RGMII_ID_MODE] = REG_FIELD(0x18, 4, 4),
> +	}, {
> +		[PHY_GMII_SEL_PORT_MODE] = REG_FIELD(0x1C, 0, 2),
> +		[PHY_GMII_SEL_RGMII_ID_MODE] = REG_FIELD(0x1C, 4, 4),
> +	},
>  };
>  
>  static const
>  struct phy_gmii_sel_soc_data phy_gmii_sel_soc_am654 = {
>  	.use_of_data = true,
> +	.features = BIT(PHY_GMII_SEL_RGMII_ID_MODE) |
> +		    BIT(PHY_GMII_SEL_FIXED_TX_DELAY),
>  	.regfields = phy_gmii_sel_fields_am654,
>  };
>  
>  static const
>  struct phy_gmii_sel_soc_data phy_gmii_sel_cpsw5g_soc_j7200 = {
>  	.use_of_data = true,
> +	.features = BIT(PHY_GMII_SEL_RGMII_ID_MODE) |
> +		    BIT(PHY_GMII_SEL_FIXED_TX_DELAY),
>  	.regfields = phy_gmii_sel_fields_am654,
>  	.extra_modes = BIT(PHY_INTERFACE_MODE_QSGMII) | BIT(PHY_INTERFACE_MODE_SGMII) |
>  		       BIT(PHY_INTERFACE_MODE_USXGMII),
> @@ -239,6 +271,8 @@ struct phy_gmii_sel_soc_data phy_gmii_sel_cpsw5g_soc_j7200 = {
>  static const
>  struct phy_gmii_sel_soc_data phy_gmii_sel_cpsw9g_soc_j721e = {
>  	.use_of_data = true,
> +	.features = BIT(PHY_GMII_SEL_RGMII_ID_MODE) |
> +		    BIT(PHY_GMII_SEL_FIXED_TX_DELAY),
>  	.regfields = phy_gmii_sel_fields_am654,
>  	.extra_modes = BIT(PHY_INTERFACE_MODE_QSGMII) | BIT(PHY_INTERFACE_MODE_SGMII),
>  	.num_ports = 8,
> @@ -248,6 +282,8 @@ struct phy_gmii_sel_soc_data phy_gmii_sel_cpsw9g_soc_j721e = {
>  static const
>  struct phy_gmii_sel_soc_data phy_gmii_sel_cpsw9g_soc_j784s4 = {
>  	.use_of_data = true,
> +	.features = BIT(PHY_GMII_SEL_RGMII_ID_MODE) |
> +		    BIT(PHY_GMII_SEL_FIXED_TX_DELAY),
>  	.regfields = phy_gmii_sel_fields_am654,
>  	.extra_modes = BIT(PHY_INTERFACE_MODE_QSGMII) | BIT(PHY_INTERFACE_MODE_SGMII) |
>  		       BIT(PHY_INTERFACE_MODE_USXGMII),

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