netdev - Re: [PATCH v2 2/2] dt-bindings: net: phy: vsc8531: document 'vsc8531,clkout-freq-mhz' property

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Date: Sat, 5 Aug 2023 23:25:31 +0300
From: Alexandru Ardelean <alex@...uggie.ro>
To: Andrew Lunn <andrew@...n.ch>
Cc: Rob Herring <robh@...nel.org>, netdev@...r.kernel.org, devicetree@...r.kernel.org, 
	linux-kernel@...r.kernel.org, davem@...emloft.net, edumazet@...gle.com, 
	kuba@...nel.org, pabeni@...hat.com, krzysztof.kozlowski+dt@...aro.org, 
	conor+dt@...nel.org, hkallweit1@...il.com, linux@...linux.org.uk, 
	olteanv@...il.com, marius.muresan@....ro
Subject: Re: [PATCH v2 2/2] dt-bindings: net: phy: vsc8531: document
 'vsc8531,clkout-freq-mhz' property

On Sun, Jul 16, 2023 at 6:07 PM Andrew Lunn <andrew@...n.ch> wrote:
>
> > So, there's the adin.c PHY driver which has a similar functionality
> > with the adin_config_clk_out().
> > Something in the micrel.c PHY driver (with
> > micrel,rmii-reference-clock-select-25-mhz); hopefully I did not
> > misread the code about that one.
> > And the at803x.c PHY driver has a 'qca,clk-out-frequency' property too.
> >
> > Now with the mscc.c driver, there is a common-ality that could use a framework.
> >
> > @Rob are you suggesting something like registering a clock provider
> > (somewhere in the PHY framework) and let the PHY drivers use it?
> > Usually, these clock signals (once enabled on startup), don't get
> > turned off; but I've worked mostly on reference designs; somewhere
> > down the line some people get different requirements.
> > These clocks get connected back to the MAC (usually), and are usually
> > like a "fixed-clock" driver.
>
> They are not necessarily fixed clocks. The clock you are adding here
> has three frequencies. Two frequencies is common for PHY devices. So
> you need to use something more than clk-fixed-rate.c. Also, mostly
> PHYs allows the clock to be gated.
>
> > In our case, turning off the clock would be needed if the PHY
> > negotiates a non-gigabit link; i.e 100 or 10 Mbps; in that case, the
> > CLKOUT signal is not needed and it can be turned off.
>
> Who does not need it? The PHY, or the MAC? If it is the MAC, it should
> really be the MAC driver which uses the common clock API to turn it
> off. Just watch out for deadlocks with phydev->lock.

The MAC needs the clock in GMII mode, when going in gigabit mode.

>
> > Maybe start out with a hook in 'struct phy_driver'?
> > Like "int (*config_clk_out)(struct phy_device *dev);" or something?
> > And underneath, this delegates to the CLK framework?
>
> Yes, have phy_device.c implement that registration/unregister of the
> clock, deal with locking, and call into the PHY driver to actually
> manipulate the clock. You missed the requested frequency in the
> function prototype. I would also call it refclk. Three is sometimes
> confusion about the different clocks.

Ack.
Then something like:
int (*config_refclk)(struct phy_device *dev, uint32_t frequency);

>
> Traditionally, clk_enable() can be called in atomic context, but that
> is not allowed with phylib, it always assume thread context. I don't
> know if the clock framework has some helpers for that, but i also
> don't see there being a real need for MAC to enable the clock in
> atomic context.
>
>         Andrew