Message-ID: <392105cb-3f73-4765-a702-7cce0c6ac62c@gmail.com>
Date: Wed, 13 Nov 2024 22:48:36 +0100
From: Heiner Kallweit <hkallweit1@...il.com>
To: Choong Yong Liang <yong.liang.choong@...ux.intel.com>,
 Andrew Lunn <andrew@...n.ch>
Cc: Russell King <linux@...linux.org.uk>,
 "David S . Miller" <davem@...emloft.net>, Eric Dumazet
 <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>,
 Paolo Abeni <pabeni@...hat.com>,
 Alexandre Torgue <alexandre.torgue@...s.st.com>,
 Jose Abreu <joabreu@...opsys.com>,
 Maxime Coquelin <mcoquelin.stm32@...il.com>, netdev@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-stm32@...md-mailman.stormreply.com,
 linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH net v1 1/2] net: phy: Introduce phy_update_eee() to update
 eee_cfg values

On 13.11.2024 11:10, Choong Yong Liang wrote:
> 
> 
> On 12/11/2024 9:04 pm, Andrew Lunn wrote:
>> On Tue, Nov 12, 2024 at 12:03:15PM +0100, Heiner Kallweit wrote:
>>> In stmmac_ethtool_op_get_eee() you have the following:
>>>
>>> edata->tx_lpi_timer = priv->tx_lpi_timer;
>>> edata->tx_lpi_enabled = priv->tx_lpi_enabled;
>>> return phylink_ethtool_get_eee(priv->phylink, edata);
>>>
>>> You have to call phylink_ethtool_get_eee() first, otherwise the manually
>>> set values will be overridden. However setting tx_lpi_enabled shouldn't
>>> be needed if you respect phydev->enable_tx_lpi.
>>
>> I agree with Heiner here, this sounds like a bug somewhere, not
>> something which needs new code in phylib. Lets understand why it gives
>> the wrong results.
>>
>>     Andrew
> Hi Russell, Andrew, and Heiner, thanks a lot for your valuable feedback.
> 
> The current implementation of the 'ethtool --show-eee' command heavily relies on the phy_ethtool_get_eee() in phy.c. The eeecfg values are set by the 'ethtool --set-eee' command and the phy_support_eee() during the initial state. The phy_ethtool_get_eee() calls eeecfg_to_eee(), which returns the eeecfg containing tx_lpi_timer, tx_lpi_enabled, and eee_enable for the 'ethtool --show-eee' command.
> 
"relies on" may be the wrong term here. There's an API definition,
and phy_ethtool_get_eee() takes care of the PHY-related kernel part,
provided that the MAC driver uses phylib.
I say "PHY-related part", because tx_lpi_timer is something relevant
for the MAC only. Therefore phylib stores the master config timer value
only, not the actual value.
The MAC driver should populate tx_lpi_timer in the get_eee() callback,
in addition to what phy_ethtool_get_eee() populates.
This may result in the master config value being overwritten with actual
value in cases where the MAC doesn't support the master config value.

One (maybe there are more) special case of tx_lpi_timer handling is
Realtek chips, as they store the LPI timer in bytes. Means whenever
the link speed changes, the actual timer value also changes implicitly.

Few values exist twice: As a master config value, and as status.
struct phy_device has the status values:
@eee_enabled: Flag indicating whether the EEE feature is enabled
@enable_tx_lpi: When True, MAC should transmit LPI to PHY

And master config values are in struct eee_cfg:

struct eee_config {
	u32 tx_lpi_timer;
	bool tx_lpi_enabled;
	bool eee_enabled;
};

And yes, it may be a little misleading that eee_enabled exists twice,
you have to be careful which one you're referring to.

ethtool handles the master config values, only "active" is a status
information.

So the MAC driver should:
- provide a link change handler in e.g. phy_connect_direct()
- this handler should:
  - use phydev->enable_tx_lpi to set whether MAC transmits LPI or not
  - use phydev->eee_cfg.tx_lpi_timer to set the timer (if the config
    value is set)

Important note:
This describes how MAC drivers *should* behave. Some don't get it right.
So part of your confusion may be caused by misbehaving MAC drivers.
One example of a MAC driver bug is what I wrote earlier about 
stmmac_ethtool_op_get_eee().

And what I write here refers to plain phylib, I don't cover phylink as
additional layer.


> The tx_lpi_timer and tx_lpi_enabled values stored in the MAC or PHY driver are not retrieved by the 'ethtool --show-eee' command.
> 
> Currently, we are facing 3 issues:
> 1. When we boot up our system and do not issue the 'ethtool --set-eee' command, and then directly issue the 'ethtool --show-eee' command, it always shows that EEE is disabled due to the eeecfg values not being set. However, in the Maxliner GPY PHY, the driver EEE is enabled. If we try to disable EEE, nothing happens because the eeecfg matches the setting required to disable EEE in ethnl_set_eee(). The phy_support_eee() was introduced to set the initial values to enable eee_enabled and tx_lpi_enabled. This would allow 'ethtool --show-eee' to show that EEE is enabled during the initial state. However, the Marvell PHY is designed to have hardware disabled EEE during the initial state. Users are required to use Ethtool to enable the EEE. phy_support_eee() does not show the correct for Marvell PHY.
> 
> 2. The 'ethtool --show-eee' command does not display the correct status, even if the link is down or the speed changes to one that does not support EEE.
> 
> 3. The tx_lpi_timer in 'ethtool --show-eee' always shows 0 if we have not used 'ethtool --set-eee' to set the values, even though the driver sets different values.
> 
> I appreciate Russell's point that eee_enabled is a user configuration bit, not a status bit. However, I am curious if tx_lpi_timer, tx_lpi_enabled, and other fields are also considered configuration bits.
> 
> According to the ethtool man page:
> --show-eee
> Queries the specified network device for its support of Energy-Efficient Ethernet (according to the IEEE 802.3az specifications)
> 
> It does not specify which fields are configuration bits and which are status bits.

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