RE: [PATCH net-next 2/2] net: stmmac: Add callbacks for DWC xpcs Energy Efficient Ethernet

-----Original Message-----
From: Russell King <linux@armlinux.org.uk>
Sent: Tuesday, 18 May, 2021 6:06 PM
To: Sit, Michael Wei Hong <redacted>
Cc: Jose.Abreu@synopsys.com; andrew@lunn.ch;
hkallweit1@gmail.com; kuba@kernel.org;
netdev@vger.kernel.org; peppe.cavallaro@st.com;
alexandre.torgue@foss.st.com; davem@davemloft.net;
mcoquelin.stm32@gmail.com; Voon, Weifeng
[off-list ref]; Ong, Boon Leong
[off-list ref]; Tan, Tee Min
[off-list ref]; vee.khee.wong@linux.intel.com;
Wong, Vee Khee [off-list ref]; linux-stm32@st-
md-mailman.stormreply.com; linux-arm-
kernel@lists.infradead.org; linux-kernel@vger.kernel.org
Subject: Re: [PATCH net-next 2/2] net: stmmac: Add callbacks for
DWC xpcs Energy Efficient Ethernet

On Mon, May 17, 2021 at 11:37:12AM +0000, Sit, Michael Wei
Hong wrote:

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From: Russell King <linux@armlinux.org.uk>

On Mon, May 17, 2021 at 05:43:32PM +0800, Michael Sit Wei

Hong

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wrote:

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Link xpcs callback functions for MAC to configure the xpcs

EEE

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feature.

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The clk_eee frequency is used to calculate the

MULT_FACT_100NS. This

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is to adjust the clock tic closer to 100ns.

Signed-off-by: Michael Sit Wei Hong

[off-list ref]

What is the initial state of the EEE configuration before the

first

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call to stmmac_ethtool_op_set_eee()? Does it reflect the

default EEE

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settings?

The register values before the first call are the default reset

values

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in the registers. The reset values assumes the clk_eee_i time

period

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is 10ns, Hence, the reset value is set to 9.
According to the register description, This value should be

programmed

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such that the clk_eee_i_time_period * (MULT_FACT_100NS + 1)

should be

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within 80 ns to 120 ns.

Since we are using a fixed 19.2MHz clk_eee, which is 52ns, we

are

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setting the value to 1.

Does that hardware default configuration match what is returned
by ethtool --show-eee ?

May I know what is the hardware default configuration that is expected
to be returned by ethtool --show-eee?
The MULT_FACT_100NS value is an internal register setting not meant
to be exposed to userspace, and only relevant when EEE is enabled.

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