netdev - Re: [PATCH net-next v4 2/7] net: dsa: microchip: Add KSZ8463 switch support to KSZ DSA driver

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Message-ID: <20250720102406.GS2459@horms.kernel.org>
Date: Sun, 20 Jul 2025 11:24:06 +0100
From: Simon Horman <horms@...nel.org>
To: Tristram.Ha@...rochip.com
Cc: Woojung Huh <woojung.huh@...rochip.com>, Andrew Lunn <andrew@...n.ch>,
	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 2/7] net: dsa: microchip: Add KSZ8463 switch
 support to KSZ DSA driver

On Fri, Jul 18, 2025 at 06:21:01PM -0700, Tristram.Ha@...rochip.com wrote:
> From: Tristram Ha <tristram.ha@...rochip.com>
> 
> KSZ8463 switch is a 3-port switch based from KSZ8863.  Its major
> difference from other KSZ SPI switches is its register access is not a
> simple continual 8-bit transfer with automatic address increase but uses
> a byte-enable mechanism specifying 8-bit, 16-bit, or 32-bit access.  Its
> registers are also defined in 16-bit format because it shares a design
> with a MAC controller using 16-bit access.  As a result some common
> register accesses need to be re-arranged.  The 64-bit access used by
> other switches needs to be broken into 2 32-bit accesses.
> 
> This patch adds the basic structure for using KSZ8463.  It cannot use the
> same regmap table for other KSZ switches as it interprets the 16-bit
> value as little-endian and its SPI commands are different.
> 
> KSZ8463's internal PHYs use standard PHY register definitions so there is
> no need to remap things.  However, the hardware has a bug that the high
> word and low word of the PHY id are swapped.  In addition the port
> registers are arranged differently so KSZ8463 has its own mapping for
> port registers and PHY registers.
> 
> Signed-off-by: Tristram Ha <tristram.ha@...rochip.com>

...

> diff --git a/drivers/net/dsa/microchip/ksz8.c b/drivers/net/dsa/microchip/ksz8.c

...

> +static inline u16 ksz8463_get_phy_addr(u16 phy, u16 reg, u16 offset)
> +{
> +	return offset + reg * 2 + phy * (P2MBCR - P1MBCR);
> +}

nit: Please do not use the inline keyword in .c files,
     unless there is a demonstrable (usually performance) reason to do so.
     Rather, let the compiler inline (or not) code as it sees fit.

...