[PATCH net v3] net: dsa: mt7530: fix enabling EEE on MT7531 switch on all boards

[Paolo Abeni]

On Mon, 2024-04-08 at 10:08 +0300, Arınç ÜNAL via B4 Relay wrote:
> From: Arınç ÜNAL <arinc.unal at arinc9.com>
> 
> The commit 40b5d2f15c09 ("net: dsa: mt7530: Add support for EEE features")
> brought EEE support but did not enable EEE on MT7531  MACs. EEE is
> enabled on MT7531 switch MACs by pulling the LAN2LED0 pin low on the board
> (bootstrapping), unsetting the EEE_DIS bit on the trap register, or setting
> the internal EEE switch bit on the CORE_PLL_GROUP4 register. Thanks to
> SkyLake Huang (黃啟澤) from MediaTek for providing information on the
> internal EEE switch bit.
> 
> There are existing boards that were not designed to pull the pin low.
> Because of that, the EEE status currently depends on the board design.
> 
> The EEE_DIS bit on the trap pertains to the LAN2LED0 pin which is usually
> used to control an LED. Once the bit is unset, the pin will be low. That
> will make the active low LED turn on. The pin is controlled by the switch
> PHY. It seems that the PHY controls the pin in the way that it inverts the
> pin state. That means depending on the wiring of the LED connected to
> LAN2LED0 on the board, the LED may be on without an active link.
> 
> To not cause this unwanted behaviour whilst enabling EEE on all boards, set
> the internal EEE switch bit on the CORE_PLL_GROUP4 register.
> 
> My testing on MT7531 shows a certain amount of traffic loss when EEE is
> enabled. That said, I haven't come across a board that enables EEE. So
> enable EEE on the switch MACs but disable EEE advertisement on the switch
> PHYs. This way, we don't change the behaviour of the majority of the boards
> that have this switch. The mediatek-ge PHY driver already disables EEE
> advertisement on the switch PHYs but my testing shows that it is somehow
> enabled afterwards. Disabling EEE advertisement before the PHY driver
> initialises keeps it off.
> 
> With this change, EEE can now be enabled using ethtool.
> 
> Fixes: 40b5d2f15c09 ("net: dsa: mt7530: Add support for EEE features")
> Reviewed-by: Florian Fainelli <florian.fainelli at broadcom.com>
> Signed-off-by: Arınç ÜNAL <arinc.unal at arinc9.com>
> ---
> Here's some information for the record. EEE could not be enabled on MT7531
> on most boards using ethtool before this. On MT7988 SoC switch, EEE is
> disabled by default but can be turned on normally using ethtool. EEE is
> enabled by default on MT7530 and there's no need to make changes on the DSA
> subdriver for it.
> ---
> Changes in v3:
> - Remove patch 2, it was revealed that it doesn't fix a bug.
> - Patch 1
>   - Use the internal EEE switch bit provided by SkyLake Huang (黃啟澤). It
>     is a better method compared to unsetting the EEE_DIS bit of the trap as
>     the latter method causes unwanted behaviour on the LED connected to the
>     pin that pertains to the EEE_DIS bit.

Since this leverages something relatively obscure, it would be great if
someone in the CC list could independently test it. Let's wait a bit
more.

Cheers,

Paolo