Problematic understanding of phy-mode in Rockchip DWMAC driver

Problematic understanding of phy-mode in Rockchip DWMAC driver

[Yao Zi]

Hi folks,

I was looking through the RGMII delay setup logic found in
rk_gmac_powerup() of dwmac-rk.c, and found its behavior is strange,

	switch (bsp_priv->phy_iface) {
	case PHY_INTERFACE_MODE_RGMII:
		dev_info(dev, "init for RGMII\n");
		if (bsp_priv->ops->set_to_rgmii)
			bsp_priv->ops->set_to_rgmii(bsp_priv,
						    bsp_priv->tx_delay,
						    bsp_priv->rx_delay);
		break;
	case PHY_INTERFACE_MODE_RGMII_ID:
		dev_info(dev, "init for RGMII_ID\n");
		if (bsp_priv->ops->set_to_rgmii)
			bsp_priv->ops->set_to_rgmii(bsp_priv, 0, 0);
		break;
	case PHY_INTERFACE_MODE_RGMII_RXID:
		dev_info(dev, "init for RGMII_RXID\n");
		if (bsp_priv->ops->set_to_rgmii)
			bsp_priv->ops->set_to_rgmii(bsp_priv,
						    bsp_priv->tx_delay, 0);
		break;
	case PHY_INTERFACE_MODE_RGMII_TXID:
		dev_info(dev, "init for RGMII_TXID\n");
		if (bsp_priv->ops->set_to_rgmii)
			bsp_priv->ops->set_to_rgmii(bsp_priv,
						    0, bsp_priv->rx_delay);
		break;
	case PHY_INTERFACE_MODE_RMII:
		dev_info(dev, "init for RMII\n");
		if (bsp_priv->ops->set_to_rmii)
			bsp_priv->ops->set_to_rmii(bsp_priv);
		break;
	default:
		dev_err(dev, "NO interface defined!\n");
	}

I don't think dwmac-rk.c does any fixup for phy_interface, so the MAC
driver always connects the PHY with unmodified phy-mode.

ethernet-controller.yaml states,

> # Device Tree describes hardware, and in this case, it describes the
> # PCB between the MAC and the PHY, if the PCB implements delays or
> # not.

So let's assume this is true for Rockchip's DWMAC glue, then the
driver's behavior could be summarized as,

phy-mode	PCB delay	Rockchip MAC delay	PHY delay[1]
rgmii		TX & RX		TX & RX			TX & RX
rgmii-id	None		None			TX & RX
rgmii-rxid	TX		TX			RX
rgmii-txid	RX		RX			TX
[1]: if available

where only the "rgmii-id" case makes sense. Other cases come with 2ns
delays added more than once, and would cause broken link.

It looks like dwmac-rk.c considers "phy-mode" to represent MAC's delay
configuration. If so, the table would look like,

phy-mode	PCB delay	Rockchip MAC delay	PHY delay[1]
rgmii		N/A		TX & RX			None
rgmii-id	N/A		None			TX & RX
rgmii-txid	N/A		TX			RX
rgmii-rxid	N/A		RX			TX

all cases have the necessary 2ns delay provided for both TX and RX
signals, however on-PCB delays made by traces couldn't be described
at all. This idea is also proved by comments in Rockchip devicetrees,
for example, rk3576-roc-pc.dts,

	&gmac0 {
		...
		/* Use rgmii-rxid mode to disable rx delay inside Soc */
		phy-mode = "rgmii-rxid";
	};

It seems for Rockchip DWMAC driver, "phy-mode" doesn't follow the
generic definition. Should we annotate in rockchip-dwmac.yaml to mention
the different usage of the property, or update both the driver and
devicetrees to align with ethernet-controller.yaml? The later would
break compatibility with existing devicetrees since there are already 15
instances of "rgmii-rxid" found in arch/arm64/boot/dts/rockchip, but
luckily most boards make use of "rgmii-id".

I only did a brief search in lore but find no related discussion, please
point out if there has already been messages around it, thanks.

Best regards,
Yao Zi

Re: Problematic understanding of phy-mode in Rockchip DWMAC driver

[Russell King (Oracle)]

On Fri, Feb 13, 2026 at 06:26:44PM +0000, Yao Zi wrote:
> Hi folks,
> 
> I was looking through the RGMII delay setup logic found in
> rk_gmac_powerup() of dwmac-rk.c, and found its behavior is strange,

dwmac-rk is very broken and is unfixable thanks to Rockchip not
understanding the RGMII interface modes used by the kernel.

It is what it is, we can't change it without causing regressions.
Please do not try to fix it.

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
FTTP is here! 80Mbps down 10Mbps up. Decent connectivity at last!

Re: Problematic understanding of phy-mode in Rockchip DWMAC driver

[Andrew Lunn]

On Fri, Feb 13, 2026 at 06:47:14PM +0000, Russell King (Oracle) wrote:
> On Fri, Feb 13, 2026 at 06:26:44PM +0000, Yao Zi wrote:
> > Hi folks,
> > 
> > I was looking through the RGMII delay setup logic found in
> > rk_gmac_powerup() of dwmac-rk.c, and found its behavior is strange,
> 
> dwmac-rk is very broken and is unfixable thanks to Rockchip not
> understanding the RGMII interface modes used by the kernel.
> 
> It is what it is, we can't change it without causing regressions.
> Please do not try to fix it.

Rockchip have recently started adding support for a new version, and
appear to of listened to what we have been saying. So it could be the
next generation of chips get this correct.

Aspeed are in a similar position, and might also get their next
generation correct.

But as Russell pointed out, we have to be very careful with any
potential changes to this code. Despite it being wrong, boards
work. We cannot fix it and cause regressions.

     Andrew

Re: Problematic understanding of phy-mode in Rockchip DWMAC driver

[Russell King (Oracle)]

On Sat, Feb 14, 2026 at 05:50:15PM +0100, Andrew Lunn wrote:
> Rockchip have recently started adding support for a new version, and
> appear to of listened to what we have been saying. So it could be the
> next generation of chips get this correct.

Have you seen any proposed code from Rockchip for their new scheme?

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
FTTP is here! 80Mbps down 10Mbps up. Decent connectivity at last!

Re: Problematic understanding of phy-mode in Rockchip DWMAC driver

[Andrew Lunn]

On Sat, Feb 14, 2026 at 07:02:08PM +0000, Russell King (Oracle) wrote:
> On Sat, Feb 14, 2026 at 05:50:15PM +0100, Andrew Lunn wrote:
> > Rockchip have recently started adding support for a new version, and
> > appear to of listened to what we have been saying. So it could be the
> > next generation of chips get this correct.
> 
> Have you seen any proposed code from Rockchip for their new scheme?

There was a patch, including a rather odd formulae to convert register
value to delay. I gave some feedback, but it has been silence
afterwards.

	Andrew

Re: Problematic understanding of phy-mode in Rockchip DWMAC driver

[Russell King (Oracle)]

On Mon, Feb 16, 2026 at 02:57:48AM +0100, Andrew Lunn wrote:
> On Sat, Feb 14, 2026 at 07:02:08PM +0000, Russell King (Oracle) wrote:
> > On Sat, Feb 14, 2026 at 05:50:15PM +0100, Andrew Lunn wrote:
> > > Rockchip have recently started adding support for a new version, and
> > > appear to of listened to what we have been saying. So it could be the
> > > next generation of chips get this correct.
> > 
> > Have you seen any proposed code from Rockchip for their new scheme?
> 
> There was a patch, including a rather odd formulae to convert register
> value to delay. I gave some feedback, but it has been silence
> afterwards.

Searching lore's netdev archive doesn't seem to bring anything up.

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
FTTP is here! 80Mbps down 10Mbps up. Decent connectivity at last!

Re: Problematic understanding of phy-mode in Rockchip DWMAC driver

[Diederik de Haas]

On Mon Feb 16, 2026 at 4:00 PM CET, Russell King (Oracle) wrote:
> On Mon, Feb 16, 2026 at 02:57:48AM +0100, Andrew Lunn wrote:
>> On Sat, Feb 14, 2026 at 07:02:08PM +0000, Russell King (Oracle) wrote:
>> > On Sat, Feb 14, 2026 at 05:50:15PM +0100, Andrew Lunn wrote:
>> > > Rockchip have recently started adding support for a new version, and
>> > > appear to of listened to what we have been saying. So it could be the
>> > > next generation of chips get this correct.
>> > 
>> > Have you seen any proposed code from Rockchip for their new scheme?
>> 
>> There was a patch, including a rather odd formulae to convert register
>> value to delay. I gave some feedback, but it has been silence
>> afterwards.
>
> Searching lore's netdev archive doesn't seem to bring anything up.

https://patch.msgid.link/b25d6eb2-e105-4060-86fa-c1a06396ca92@lunn.ch/

Re: Problematic understanding of phy-mode in Rockchip DWMAC driver

[Chaoyi Chen]

Hi all,

On 2/17/2026 1:21 AM, Diederik de Haas wrote:
> On Mon Feb 16, 2026 at 4:00 PM CET, Russell King (Oracle) wrote:
>> On Mon, Feb 16, 2026 at 02:57:48AM +0100, Andrew Lunn wrote:
>>> On Sat, Feb 14, 2026 at 07:02:08PM +0000, Russell King (Oracle) wrote:
>>>> On Sat, Feb 14, 2026 at 05:50:15PM +0100, Andrew Lunn wrote:
>>>>> Rockchip have recently started adding support for a new version, and
>>>>> appear to of listened to what we have been saying. So it could be the
>>>>> next generation of chips get this correct.
>>>>
>>>> Have you seen any proposed code from Rockchip for their new scheme?
>>>
>>> There was a patch, including a rather odd formulae to convert register
>>> value to delay. I gave some feedback, but it has been silence
>>> afterwards.
>>
>> Searching lore's netdev archive doesn't seem to bring anything up.
> 
> https://patch.msgid.link/b25d6eb2-e105-4060-86fa-c1a06396ca92@lunn.ch/
> 

I am the author of this patch series. My understanding is that
"rgmii-id" should be adopted first, and for any delays that may
need to be introduced, they should be implemented in the PHY rather
than in the GMAC, although I did try to do so. 

Did I miss something?

-- 
Best, 
Chaoyi

Re: Problematic understanding of phy-mode in Rockchip DWMAC driver

[Yao Zi]

On Fri, Feb 13, 2026 at 06:47:14PM +0000, Russell King (Oracle) wrote:
> On Fri, Feb 13, 2026 at 06:26:44PM +0000, Yao Zi wrote:
> > Hi folks,
> > 
> > I was looking through the RGMII delay setup logic found in
> > rk_gmac_powerup() of dwmac-rk.c, and found its behavior is strange,
> 
> dwmac-rk is very broken and is unfixable thanks to Rockchip not
> understanding the RGMII interface modes used by the kernel.
> 
> It is what it is, we can't change it without causing regressions.
> Please do not try to fix it.

Thanks for confirming. I understand concerns about regressions and
agree keeping the driver/dts as-is is better.

However, should we mention the difference between "phy-mode" defined
ethernet-controller.yaml and "phy-mode" understood by dwmac-rk
driver in rockchip-dwmac.yaml to avoid confusion in the future?

Regards,
Yao Zi

> -- 
> RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
> FTTP is here! 80Mbps down 10Mbps up. Decent connectivity at last!

Re: Problematic understanding of phy-mode in Rockchip DWMAC driver

[Andrew Lunn]

On Mon, Feb 16, 2026 at 04:44:27AM +0000, Yao Zi wrote:
> On Fri, Feb 13, 2026 at 06:47:14PM +0000, Russell King (Oracle) wrote:
> > On Fri, Feb 13, 2026 at 06:26:44PM +0000, Yao Zi wrote:
> > > Hi folks,
> > > 
> > > I was looking through the RGMII delay setup logic found in
> > > rk_gmac_powerup() of dwmac-rk.c, and found its behavior is strange,
> > 
> > dwmac-rk is very broken and is unfixable thanks to Rockchip not
> > understanding the RGMII interface modes used by the kernel.
> > 
> > It is what it is, we can't change it without causing regressions.
> > Please do not try to fix it.
> 
> Thanks for confirming. I understand concerns about regressions and
> agree keeping the driver/dts as-is is better.
> 
> However, should we mention the difference between "phy-mode" defined
> ethernet-controller.yaml and "phy-mode" understood by dwmac-rk
> driver in rockchip-dwmac.yaml to avoid confusion in the future?

I've been telling DT developers to set the correct phy-mode,
'rgmii-id', and the vendor properties for MAC delays to 0. That works,
and it consistent with the documentation.

As far as i know, dwmac-rk only gets things wrong when you try to get
the MAC to add the 2ns delays. And that is not a recommended
configuration. So i don't think it is too important to document a not
recommended configuration is broken.

	Andrew