Subject: Re: [PATCH RFC net-next 00/23] net: phylink managed EEE support

From: "Russell King (Oracle)" <[email-masked]>
Date: Tue, 26 Nov 2024 13:01:11 +0000

On Tue, Nov 26, 2024 at 12:51:36PM +0000, Russell King (Oracle) wrote:
> Patch 11 adds phylink managed EEE support. Two new MAC APIs are added,
> to enable and disable LPI. The enable method is passed the LPI timer
> setting which it is expected to program into the hardware, and also a
> flag ehther the transmit clock should be stopped.
> 
>  *** There are open questions here. Eagle eyed reviewers will notice
>    pl->config->lpi_interfaces. There are MACs out there which only
>    support LPI signalling on a subset of their interface types. Phylib
>    doesn't understand this. I'm handling this at the moment by simply
>    not activating LPI at the MAC, but that leads to ethtool --show-eee
>    suggesting that EEE is active when it isn't.
>  *** Should we pass the phy_interface_t to these functions?
>  *** Should mac_enable_tx_lpi() be allowed to fail if the MAC doesn't
>    support the interface mode?

There is another point to raise here - should we have a "validate_eee"
method in struct phylink_mac_ops so that MAC drivers can validate
settings such as the tx_lpi_timer value can be programmed into the
hardware?

We do have the situation on Marvell platforms where the programmed
value depends on the MAC speed, and is only 8 bit, which makes
validating its value rather difficult - at 1G speeds, it's a
resolution of 1us so we can support up to 255us. At 100M speeds,
it's 10us, supporting up to 2.55ms. This makes it awkward to be able
to validate the set_eee() settings are sane for the hardware. Should
Marvell platforms instead implement a hrtimer above this? That sounds
a bit problematical to manage sanely.

-- 
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