netdev - Re: [PATCH net-next v4 3/7] net: dsa: microchip: Transform register for use with KSZ8463

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Message-ID: <4dd544ad-fa71-4759-bc23-d1dd7f554eb8@lunn.ch>
Date: Sun, 20 Jul 2025 17:56:52 +0200
From: Andrew Lunn <andrew@...n.ch>
To: Tristram.Ha@...rochip.com
Cc: Woojung Huh <woojung.huh@...rochip.com>,
	Vladimir Oltean <olteanv@...il.com>, Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>,
	Maxime Chevallier <maxime.chevallier@...tlin.com>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Marek Vasut <marex@...x.de>, UNGLinuxDriver@...rochip.com,
	devicetree@...r.kernel.org, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next v4 3/7] net: dsa: microchip: Transform register
 for use with KSZ8463

> +static inline bool ksz_is_ksz8463(struct ksz_device *dev)
> +{
> +	return dev->chip_id == KSZ8463_CHIP_ID;
> +}
> +
> +static inline u32 reg8(struct ksz_device *dev, u32 reg)
> +{
> +	if (ksz_is_ksz8463(dev))
> +		return ((reg >> 2) << 4) | (1 << (reg & 3));
> +	return reg;
> +}
> +
> +static inline u32 reg16(struct ksz_device *dev, u32 reg)
> +{
> +	if (ksz_is_ksz8463(dev))
> +		return ((reg >> 2) << 4) | (reg & 2 ? 0x0c : 0x03);
> +	return reg;
> +}
> +
> +static inline u32 reg32(struct ksz_device *dev, u32 reg)
> +{
> +	if (ksz_is_ksz8463(dev))
> +		return ((reg >> 2) << 4) | 0xf;
> +	return reg;
> +}
> +
>  static inline int ksz_read8(struct ksz_device *dev, u32 reg, u8 *val)
>  {
>  	unsigned int value;
> -	int ret = regmap_read(ksz_regmap_8(dev), reg, &value);
> +	int ret = regmap_read(ksz_regmap_8(dev), reg8(dev, reg), &value);

I'm wondering if there is a less intrusive way to do this. When you
create a regmap, you can optionally pass it methods to use for
read/write/update etc.

struct regmap_config {
...
	int (*reg_read)(void *context, unsigned int reg, unsigned int *val);
	int (*reg_write)(void *context, unsigned int reg, unsigned int val);
	int (*reg_update_bits)(void *context, unsigned int reg,
			       unsigned int mask, unsigned int val);

Could you provide your own methods for the ksz8463 which perform the
register modification, and then call the normal regmap SPI function to
do the operation?

If you cannot get direct access to the regmap SPI functions, you can
stack one regmap on top of another regmap. Have the top regmap do the
register modifications, and then call a normal SPI regmap to do the
read/write.

What i don't like about the current code is that developers adding new
code could miss they need to add reg8().. to all regmap calls. So
ideally you want to hide that away so they don't need to care, it just
works.

	Andrew