Re: [PATCH 2/9] net: ethernet: mtk_eth_soc: set MDIO bus clock frequency

[Vladimir Oltean <olteanv@gmail.com>]

On Fri, Feb 03, 2023 at 07:01:01AM +0000, Daniel Golle wrote:
> Set MDIO bus clock frequency and allow setting a custom maximum
> frequency from device tree.
> 
> Signed-off-by: Daniel Golle <daniel@makrotopia.org>
> ---
>  drivers/net/ethernet/mediatek/mtk_eth_soc.c | 25 +++++++++++++++++++++
>  drivers/net/ethernet/mediatek/mtk_eth_soc.h |  5 +++++
>  2 files changed, 30 insertions(+)
> 
> diff --git a/drivers/net/ethernet/mediatek/mtk_eth_soc.c b/drivers/net/ethernet/mediatek/mtk_eth_soc.c
> index a44ffff48c7b..9050423821dc 100644
> --- a/drivers/net/ethernet/mediatek/mtk_eth_soc.c
> +++ b/drivers/net/ethernet/mediatek/mtk_eth_soc.c
> @@ -790,7 +790,9 @@ static const struct phylink_mac_ops mtk_phylink_ops = {
>  static int mtk_mdio_init(struct mtk_eth *eth)
>  {
>  	struct device_node *mii_np;
> +	int clk = 25000000, max_clk = 2500000, divider = 1;

Would be good if constant values (clk) weren't put in variables.

>  	int ret;
> +	u32 val;
>  
>  	mii_np = of_get_child_by_name(eth->dev->of_node, "mdio-bus");
>  	if (!mii_np) {
> @@ -818,6 +820,29 @@ static int mtk_mdio_init(struct mtk_eth *eth)
>  	eth->mii_bus->parent = eth->dev;
>  
>  	snprintf(eth->mii_bus->id, MII_BUS_ID_SIZE, "%pOFn", mii_np);
> +
> +	if (!of_property_read_u32(mii_np, "clock-frequency", &val))
> +		max_clk = val;

Checking for valid range? There should also probably be a dt-bindings
patch for this.

> +
> +	while (clk / divider > max_clk) {
> +		if (divider >= 63)
> +			break;
> +
> +		divider++;
> +	};

uhm, "divider = min(DIV_ROUND_UP(25000000, max_clk), 63);"? I don't
think the compiler is smart enough to optimize away this loop.

> +
> +	val = mtk_r32(eth, MTK_PPSC);
> +	val |= PPSC_MDC_TURBO;
> +	mtk_w32(eth, val, MTK_PPSC);

What does "TURBO" do and why do you set it unconditionally?

> +
> +	/* Configure MDC Divider */
> +	val = mtk_r32(eth, MTK_PPSC);
> +	val &= ~PPSC_MDC_CFG;
> +	val |= FIELD_PREP(PPSC_MDC_CFG, divider);
> +	mtk_w32(eth, val, MTK_PPSC);
> +
> +	dev_dbg(eth->dev, "MDC is running on %d Hz\n", clk / divider);
> +
>  	ret = of_mdiobus_register(eth->mii_bus, mii_np);
>  
>  err_put_node:
> diff --git a/drivers/net/ethernet/mediatek/mtk_eth_soc.h b/drivers/net/ethernet/mediatek/mtk_eth_soc.h
> index 7230dcb29315..724815ae18a0 100644
> --- a/drivers/net/ethernet/mediatek/mtk_eth_soc.h
> +++ b/drivers/net/ethernet/mediatek/mtk_eth_soc.h
> @@ -363,6 +363,11 @@
>  #define RX_DMA_VTAG_V2		BIT(0)
>  #define RX_DMA_L4_VALID_V2	BIT(2)
>  
> +/* PHY Polling and SMI Master Control registers */
> +#define MTK_PPSC		0x10000
> +#define PPSC_MDC_CFG		GENMASK(29, 24)
> +#define PPSC_MDC_TURBO		BIT(20)
> +
>  /* PHY Indirect Access Control registers */
>  #define MTK_PHY_IAC		0x10004
>  #define PHY_IAC_ACCESS		BIT(31)
> -- 
> 2.39.1
>