linux-kernel - Re: [PATCH v2 net] net: phy: micrel: Dynamically control external clock of KSZ PHY

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Message-ID: <003d5029-2339-4e18-b632-be35384b2f7a@lunn.ch>
Date: Mon, 2 Dec 2024 15:48:54 +0100
From: Andrew Lunn <andrew@...n.ch>
To: Wei Fang <wei.fang@....com>
Cc: hkallweit1@...il.com, linux@...linux.org.uk, davem@...emloft.net,
	edumazet@...gle.com, kuba@...nel.org, pabeni@...hat.com,
	florian.fainelli@...adcom.com, heiko.stuebner@...rry.de,
	frank.li@....com, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, imx@...ts.linux.dev
Subject: Re: [PATCH v2 net] net: phy: micrel: Dynamically control external
 clock of KSZ PHY

On Mon, Dec 02, 2024 at 04:45:35PM +0800, Wei Fang wrote:
> On the i.MX6ULL-14x14-EVK board, enet1_ref and enet2_ref are used as the
> clock sources for two external KSZ PHYs. However, after closing the two
> FEC ports, the clk_enable_count of the enet1_ref and enet2_ref clocks is
> not 0. The root cause is that since the commit 985329462723 ("net: phy:
> micrel: use devm_clk_get_optional_enabled for the rmii-ref clock"), the
> external clock of KSZ PHY has been enabled when the PHY driver probes,
> and it can only be disabled when the PHY driver is removed. This causes
> the clock to continue working when the system is suspended or the network
> port is down.

The referenced commit is a one liner:

@@ -2001,7 +2001,7 @@ static int kszphy_probe(struct phy_device *phydev)
 
        kszphy_parse_led_mode(phydev);
 
-       clk = devm_clk_get(&phydev->mdio.dev, "rmii-ref");
+       clk = devm_clk_get_optional_enabled(&phydev->mdio.dev, "rmii-ref");
        /* NOTE: clk may be NULL if building without CONFIG_HAVE_CLK */

and here you are adding 103 lines as a fix. This seems out of
proportion. Did this truly work before this change?

The commit message says:

    While the external clock input will most likely be enabled, it's not
    guaranteed and clk_get_rate in some suppliers will even just return
    valid results when the clock is running.

So it seems like a much simpler fix is to put a
clock_enable/clock_disable around clk_get_rate.

	Andrew