linux-kernel - Re: [PATCH 2/9] net: ethernet: mtk_eth

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Date:   Fri, 3 Feb 2023 15:06:39 +0100
From:   Andrew Lunn <andrew@...n.ch>
To:     Daniel Golle <daniel@...rotopia.org>
Cc:     netdev@...r.kernel.org, linux-mediatek@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Russell King <linux@...linux.org.uk>,
        Heiner Kallweit <hkallweit1@...il.com>,
        Lorenzo Bianconi <lorenzo@...nel.org>,
        Mark Lee <Mark-MC.Lee@...iatek.com>,
        John Crispin <john@...ozen.org>, Felix Fietkau <nbd@....name>,
        AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>,
        Matthias Brugger <matthias.bgg@...il.com>,
        DENG Qingfang <dqfext@...il.com>,
        Landen Chao <Landen.Chao@...iatek.com>,
        Sean Wang <sean.wang@...iatek.com>,
        Paolo Abeni <pabeni@...hat.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        "David S. Miller" <davem@...emloft.net>,
        Vladimir Oltean <olteanv@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        Jianhui Zhao <zhaojh329@...il.com>,
        Bjørn Mork <bjorn@...k.no>
Subject: Re: [PATCH 2/9] net: ethernet: mtk_eth_soc: set MDIO bus clock
 frequency

>  static int mtk_mdio_init(struct mtk_eth *eth)
>  {
>  	struct device_node *mii_np;
> +	int clk = 25000000, max_clk = 2500000, divider = 1;
>  	int ret;
> +	u32 val;

Reverse Christmas tree please.

> +
> +	if (!of_property_read_u32(mii_np, "clock-frequency", &val))
> +		max_clk = val;
> +
> +	while (clk / divider > max_clk) {
> +		if (divider >= 63)
> +			break;
> +
> +		divider++;
> +	};

Please add some range checks here. Return -EINVAL if val > max_clock.
Also, if divider = 63 indicating the requested clock is too slow.

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

Can these two writes to MTK_PPSC be combined into one? 

val |= FIELD_PREP(PPSC_MDC_CFG, divider) | PPSC_MDC_TURBO;

    Andrew