netdev - Re: [PATCH v2 3/3] net: mdio: mdio-thunder: support for clock-freq attribute

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Date:   Sun, 5 Jun 2022 05:24:33 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     Piyush Malgujar <pmalgujar@...vell.com>
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        krzysztof.kozlowski+dt@...aro.org, devicetree@...r.kernel.org,
        cchavva@...vell.com, deppel@...vell.com,
        Heiner Kallweit <hkallweit1@...il.com>,
        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>
Subject: Re: [PATCH v2 3/3] net: mdio: mdio-thunder: support for clock-freq
 attribute

> +static inline u32 clk_freq(u32 phase)

Please keep with the naming scheme in the rest of the driver, 
thunder_mdiobus_clk_freq()

> +{
> +	return (100000000U / (2 * (phase)));
> +}
> +
> +static inline u32 calc_sample(u32 phase)
> +{

thunder_mdiobus_calc_sample()

> +	return (2 * (phase) - 3);
> +}
> +
> +static u32 _config_clk(u32 req_freq, u32 *phase, u32 *sample)

thunder_mdiobus_config_clk().

> +{
> +	unsigned int p;
> +	u32 freq = 0, freq_prev;
> +
> +	for (p = PHASE_MIN; p < PHASE_DFLT; p++) {
> +		freq_prev = freq;
> +		freq = clk_freq(p);
> +
> +		if (req_freq >= freq)
> +			break;
> +	}
> +
> +	if (p == PHASE_DFLT)
> +		freq = clk_freq(PHASE_DFLT);
> +
> +	if (p == PHASE_MIN || p == PHASE_DFLT)
> +		goto out;
> +
> +	/* Check which clock value from the identified range
> +	 * is closer to the requested value
> +	 */
> +	if ((freq_prev - req_freq) < (req_freq - freq)) {
> +		p = p - 1;
> +		freq = freq_prev;
> +	}
> +out:
> +	*phase = p;
> +	*sample = calc_sample(p);
> +	return freq;
> +}
> +
>  static int thunder_mdiobus_pci_probe(struct pci_dev *pdev,
>  				     const struct pci_device_id *ent)
>  {
> @@ -56,6 +101,7 @@ static int thunder_mdiobus_pci_probe(struct pci_dev *pdev,
>  	i = 0;
>  	device_for_each_child_node(&pdev->dev, fwn) {
>  		struct resource r;
> +		u32 req_clk_freq;
>  		struct mii_bus *mii_bus;
>  		struct cavium_mdiobus *bus;
>  		union cvmx_smix_clk smi_clk;
> @@ -90,6 +136,23 @@ static int thunder_mdiobus_pci_probe(struct pci_dev *pdev,
>  
>  		smi_clk.u64 = oct_mdio_readq(bus->register_base + SMI_CLK);
>  		smi_clk.s.clk_idle = 1;
> +
> +		if (!of_property_read_u32(node, "clock-frequency", &req_clk_freq)) {
> +			u32 phase, sample;
> +
> +			dev_dbg(&pdev->dev, "requested bus clock frequency=%d\n",
> +				req_clk_freq);
> +
> +			bus->clk_freq = _config_clk(req_clk_freq,
> +						    &phase, &sample);
> +
> +			smi_clk.s.phase = phase;
> +			smi_clk.s.sample_hi = (sample >> 4) & 0x1f;
> +			smi_clk.s.sample = sample & 0xf;
> +		} else {
> +			bus->clk_freq = clk_freq(PHASE_DFLT);
> +		}

You can make this simpler by setting req_clk_freq to your odd
default. Then call of_property_read_u32(). If the property is not
defined, the value of req_clk_freq will not be changed, and the
calculation should come out with the correct value.

	    Andrew