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

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>
---

[...]

[...]

+/*
+ * 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