Re: [PATCH net-next v12 3/4] net: dsa: microchip: Support Microchip KSZ8995XA / KS8995XA

[Nicolai Buchwitz <nb@tipi-net.de>]

Hi Linus

On 11.9.2026 11:09, Linus Walleij wrote:
> This adds support for the Microchip KSZ8995XA also known as the
> Micrel KS8995XA switch to the KSZ driver.
> 
> The KSZ8995XA shares family ID 0x95 and chip-ID nibble 0x0 with
> the KS8995MA, so hardware detection cannot distinguish them. The
> legacy "micrel,ks8995" compatible is therefore treated as KSZ8995XA.
> No KS8995MA users are known, and KS8995E has no documented SPI
> management interface. Neither MA nor E has been verified with this
> driver.
> 
> The helper macros are named ksz_is_ksz8995xa() to make it
> possible to add E and MA support in the future.
> 
> Wait for the self-clearing per-port PHY reset bits before continuing
> with switch setup. Poll each port for up to 600 ms and allow an
> additional millisecond for the PHYs to settle.
> 
> The KSZ8995XA has eight global TOS priority registers with one
> bit per DSCP code point, providing two internal priority levels.
> The registers are ordered in the opposite direction from the
> other KSZ8 switches. Describe the two priorities in the chip
> data, then augment the DCB helpers for this.
> 
> Practical testing also shows that its packet-size control bits use
> the same semantics as the other KSZ8 switches. The polarity in the
> manual appears to be wrong and makes the switch hang on big packets.
> 
> The legacy KS8995 driver also matches the Micrel compatibles for
> KSZ8864 and KSZ8795. Add these to the KSZ SPI driver here and use
> an exact tristate dependency to make the drivers mutually exclusive.
> This transfers ownership atomically, avoiding module probe races and
> gaps in driver coverage between patches.
> 
> Assisted-by: LLM
> Signed-off-by: Linus Walleij <linusw@kernel.org>
> ---

> [...]

> diff --git a/drivers/net/dsa/microchip/ksz8.c 
> b/drivers/net/dsa/microchip/ksz8.c
> index 941ae9f66f70..4acce01ca063 100644
> --- a/drivers/net/dsa/microchip/ksz8.c
> +++ b/drivers/net/dsa/microchip/ksz8.c

> [...]

> 
> +/*
> + * Restricted operations for KSZ8995XA, so many things are not 
> supported
> + * by this old switch that we need diet DSA operations.
> + */
> +const struct dsa_switch_ops ksz8995xa_switch_ops = {
> +	.get_tag_protocol	= ksz8995xa_get_tag_protocol,
> +	.setup			= ksz8_setup,
> +	.teardown		= ksz_teardown,
> +	.phy_read		= ksz8_phy_read16,
> +	.phy_write		= ksz8_phy_write16,
> +	.phylink_get_caps	= ksz8_phylink_get_caps,
> +	.port_setup		= ksz8_dsa_port_setup,
> +	.port_bridge_join	= ksz_port_bridge_join,
> +	.port_bridge_leave	= ksz_port_bridge_leave,
> +	.port_set_mac_address	= ksz_port_set_mac_address,
> +	.port_stp_state_set	= ksz_port_stp_state_set,
> +	.port_pre_bridge_flags	= ksz_port_pre_bridge_flags,
> +	.port_bridge_flags	= ksz_port_bridge_flags,
> +	.port_fast_age		= ksz8_flush_dyn_mac_table,


KSZ8995XA datasheet [1] (table 4-2) states fast-age enable as reg 0x03 
bit 1,
but ksz8_flush_dyn_mac_table() sets reg 0x02 bit 5. It needs an override
similar to the existing one for KSZ8463, but accounting for XA's 800 us
ageing time.

> +	.port_mirror_add	= ksz8_port_mirror_add,
> +	.port_mirror_del	= ksz8_port_mirror_del,
> +	.port_change_mtu	= ksz8995xa_change_mtu,
> +	.port_max_mtu		= ksz88xx_max_mtu,
> +	.port_get_default_prio	= ksz_port_get_default_prio,
> +	.port_set_default_prio	= ksz_port_set_default_prio,
> +	.port_get_dscp_prio	= ksz_port_get_dscp_prio,
> +	.port_add_dscp_prio	= ksz_port_add_dscp_prio,
> +	.port_del_dscp_prio	= ksz_port_del_dscp_prio,
> +	.port_get_apptrust	= ksz_port_get_apptrust,
> +	.port_set_apptrust	= ksz_port_set_apptrust,

If I read the datasheet correctly, PCP and DSCP priorities are or-ed,
but ksz_port_set_apptrust() accepts both to be set (with PCP taking 
precedence).
Not sure if this would break anything though ...

The other things look fine to me.

> +};
> +

> [...]

[1] 
https://ww1.microchip.com/downloads/en/DeviceDoc/KSZ8995XA-Integrated-5-Port-10-100-QoS-Switch-DS00003677A.pdf

Thanks,
Nicolai