linux-kernel - Re: [net-next PATCH v11 5/9] mfd: an8855: Add support for Airoha AN8855 Switch MFD

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Message-ID: <20241210211529.osgzd54flq646bcr@skbuf>
Date: Tue, 10 Dec 2024 23:15:29 +0200
From: Vladimir Oltean <olteanv@...il.com>
To: Christian Marangi <ansuelsmth@...il.com>
Cc: Lee Jones <lee@...nel.org>, Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>,
	Andrew Lunn <andrew+netdev@...n.ch>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Srinivas Kandagatla <srinivas.kandagatla@...aro.org>,
	Heiner Kallweit <hkallweit1@...il.com>,
	Russell King <linux@...linux.org.uk>,
	Matthias Brugger <matthias.bgg@...il.com>,
	AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>,
	linux-arm-kernel@...ts.infradead.org,
	linux-mediatek@...ts.infradead.org, netdev@...r.kernel.org,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
	upstream@...oha.com
Subject: Re: [net-next PATCH v11 5/9] mfd: an8855: Add support for Airoha
 AN8855 Switch MFD

On Mon, Dec 09, 2024 at 02:44:22PM +0100, Christian Marangi wrote:
> +int an8855_mii_set_page(struct an8855_mfd_priv *priv, u8 phy_id,
> +			u8 page) __must_hold(&priv->bus->mdio_lock)
> +{
> +	struct mii_bus *bus = priv->bus;
> +	int ret;
> +
> +	ret = __mdiobus_write(bus, phy_id, AN8855_PHY_SELECT_PAGE, page);
> +	if (ret < 0)
> +		dev_err_ratelimited(&bus->dev,
> +				    "failed to set an8855 mii page\n");
> +
> +	/* Cache current page if next mii read/write is for switch */
> +	priv->current_page = page;
> +	return ret < 0 ? ret : 0;
> +}
> +EXPORT_SYMBOL_GPL(an8855_mii_set_page);

You could keep the implementation more contained, and you could avoid
exporting an8855_mii_set_page() and an8855_mfd_priv to the MDIO
passthrough driver, if you implement a virtual regmap and give it to the
MDIO passthrough child MFD device.

If this bus supports only clause 22 accesses (and it looks like it does),
you could expose a 16-bit regmap with a linear address space of 32 MDIO
addresses x 65536 registers. The bus->read() of the MDIO bus passthrough
just performs regmap_read(), and bus->write() just performs regmap_write().
The MFD driver decodes the regmap address into a PHY address and a regnum,
and performs the page switching locally, if needed.