Re: [PATCH v2 2/3] net: phy: Add helper for fixing RGMII PHY mode based on internal mac delay

[Andrew Lunn <andrew@lunn.ch>]

On Mon, Oct 20, 2025 at 05:54:58PM +0800, Inochi Amaoto wrote:
> The "phy-mode" property of devicetree indicates whether the PCB has
> delay now, which means the mac needs to modify the PHY mode based
> on whether there is an internal delay in the mac.
> 
> This modification is similar for many ethernet drivers. To simplify
> code, define the helper phy_fix_phy_mode_for_mac_delays(speed, mac_txid,
> mac_rxid) to fix PHY mode based on whether mac adds internal delay.
> 
> Signed-off-by: Inochi Amaoto <inochiama@gmail.com>
> ---
>  drivers/net/phy/phy-core.c | 43 ++++++++++++++++++++++++++++++++++++++
>  include/linux/phy.h        |  3 +++
>  2 files changed, 46 insertions(+)
> 
> diff --git a/drivers/net/phy/phy-core.c b/drivers/net/phy/phy-core.c
> index 605ca20ae192..4f258fb409da 100644
> --- a/drivers/net/phy/phy-core.c
> +++ b/drivers/net/phy/phy-core.c
> @@ -101,6 +101,49 @@ const char *phy_rate_matching_to_str(int rate_matching)
>  }
>  EXPORT_SYMBOL_GPL(phy_rate_matching_to_str);
> 
> +/**
> + * phy_fix_phy_mode_for_mac_delays - Convenience function for fixing PHY
> + * mode based on whether mac adds internal delay
> + *
> + * @interface: The current interface mode of the port
> + * @mac_txid: True if the mac adds internal tx delay
> + * @mac_rxid: True if the mac adds internal rx delay
> + *
> + * Return fixed PHY mode, or PHY_INTERFACE_MODE_NA if the interface can
> + * not apply the internal delay
> + */

I think a helper like this is a good idea. But there are a couple of
things i don't like about this implementation.

I don't like returning PHY_INTERFACE_MODE_NA on error. I would prefer
-EINVAL.  of_get_phy_mode() passed a phy_interface_t *, and returns an
errno. The same would be good here.

I find:

phy_fix_phy_mode_for_mac_delays(interface, true, false)

hard to read. You cannot see what these true/false mean. Which is Rx
and which is Tx?

Rather than true false, how about passing an
PHY_INTERFACE_MODE_RGMII_* values?

PHY_INTERFACE_MODE_RGMII_ID would indicate the MAC is doing both
delays.  PHY_INTERFACE_MODE_RGMII_RXID the MAC is implementing the RX
delay? I'm open to other ideas here.

	Andrew