linux-kernel - Re: [net-next 4/4] net: ftgmac100: add RGMII delay for AST2600

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Message-ID: <Z9gC2vz2w5dfZsum@shell.armlinux.org.uk>
Date: Mon, 17 Mar 2025 11:09:14 +0000
From: "Russell King (Oracle)" <linux@...linux.org.uk>
To: Maxime Chevallier <maxime.chevallier@...tlin.com>
Cc: Jacky Chou <jacky_chou@...eedtech.com>, andrew+netdev@...n.ch,
	davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org,
	pabeni@...hat.com, robh@...nel.org, krzk+dt@...nel.org,
	conor+dt@...nel.org, joel@....id.au, andrew@...econstruct.com.au,
	ratbert@...aday-tech.com, netdev@...r.kernel.org,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-aspeed@...ts.ozlabs.org,
	BMC-SW@...eedtech.com
Subject: Re: [net-next 4/4] net: ftgmac100: add RGMII delay for AST2600

On Mon, Mar 17, 2025 at 09:53:33AM +0100, Maxime Chevallier wrote:
> So this goes completely against the naming of the property. It has the
> -ps suffix, so you would expect to have picoseconds values passed, and
> not an arbiraty index.
> 
> Take a look at other drivers, you should accept picseconds values from
> these properties, then compute the relevant index in the driver. That
> index should be something internal to your driver.
> 
> An example here :
> 
> https://elixir.bootlin.com/linux/v6.14-rc6/source/drivers/net/ethernet/microchip/sparx5/lan969x/lan969x_rgmii.c#L51

Another example would be drivers/net/phy/adin.c::adin_get_reg_value()
and associated functions - these lookup a DT property and then look
that up in a table to convert it to a register value.

I suspect that's something which could become generic, as I suspect
most hardware isn't going to accept a picosecond value, but be a
choice of N different options.

-- 
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