Re: [PATCH net-next v3 4/5] net: dsa: microchip: Support Microchip KSZ8995XA / KS8995XA

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [High] The KSZ8995XA PHY register emulation incorrectly maps and overwrites fundamental port control bits, disabling RX/TX and MAC learning.
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commit 2e706ae441971159b4241c28e24cf8f143178ad5
Author: Linus Walleij <linusw@kernel.org>

net: dsa: microchip: Support Microchip KSZ8995XA / KS8995XA

This adds support for the Microchip KSZ8995XA also known as the
Micrel KS8995XA switch to the KSZ driver.

> diff --git a/drivers/net/dsa/microchip/ksz_common.c b/drivers/net/dsa/microchip/ksz_common.c
> index 57c8abfe0147d..ac27beb3054bd 100644
> --- a/drivers/net/dsa/microchip/ksz_common.c
> +++ b/drivers/net/dsa/microchip/ksz_common.c
[ ... ]
> @@ -554,6 +554,20 @@ static const u8 ksz8895_shifts[] = {
>  	[DYNAMIC_MAC_SRC_PORT]		= 24,
>  };
>  
> +static const u16 ksz8995xa_regs[] = {
> +	[REG_SW_MAC_ADDR]		= 0x68,
> +	[P_FORCE_CTRL]			= 0x0C,
> +	[P_LINK_STATUS]			= 0x0E,
> +	[P_LOCAL_CTRL]			= 0x0C,
> +	[P_NEG_RESTART_CTRL]		= 0x0D,

[Severity: High]
Will this register mapping inadvertently disable RX/TX and MAC learning?

The newly introduced ksz8995xa_regs array maps P_LOCAL_CTRL and P_FORCE_CTRL
to 0x0C, and P_NEG_RESTART_CTRL to 0x0D. The driver's PHY emulation
functions (ksz8_w_phy and ksz8_w_phy_bmcr) apply KSZ8795-specific bitmasks
to these offsets.

On the KSZ8995XA, offset 0x0C resolves to Port Control 12 (e.g., 0x1C for
Port 1), where BIT 4 is Receive Enable and BIT 3 is Transmit Enable. When
updating MII_ADVERTISE, the emulation applies PORT_AUTO_NEG_SYM_PAUSE (BIT 4)
and PORT_AUTO_NEG_100BTX_FD (BIT 3). Clearing these advertisement bits
appears to inadvertently disable RX and TX on the port.

Similarly, setting PORT_FORCE_FULL_DUPLEX (BIT 5) via MII_BMCR sets Learning
Disable. When phylink automatically configures the PHY on startup, these
writes could execute and completely break the switch port's network
functionality.

> +	[P_REMOTE_STATUS]		= 0x0E,
> +	[P_SPEED_STATUS]		= 0x09,
> +	[P_STP_CTRL]			= 0x02,
> +	[S_START_CTRL]			= 0x01,
> +	[S_BROADCAST_CTRL]		= 0x06,
> +	[S_MULTICAST_CTRL]		= 0x04,
> +};

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Sashiko AI review · https://sashiko.dev/#/patchset/20260526-ks8995-to-ksz8-v3-0-c530f651989f@kernel.org?part=4