Re: [PATCH net-next v5] net: dsa: microchip: enable the SGMII port of the KSZ9897S

[netdev-bot+sashiko@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential
issue(s) to consider:

Critical: 0 · High: 0 · Medium: 1 · Low: 0

- [Medium] Public interface defect: `KSZ9897S_CHIP_ID` (0x00989701) is
  added to `enum ksz_chip_id` in include/linux/platform_data/microchip-…

--

net: dsa: microchip: enable the SGMII port of the KSZ9897S

This adds a KSZ9897S chip_data entry with .sgmii_port = 7 and selects it in
ksz_switch_register() by reading the read-only bit 7 of the port 7 XMII
control 0 register, while leaving dev->chip_id at the shared KSZ9897 value.
A new KSZ9897S_CHIP_ID is added to enum ksz_chip_id to tag that entry.

> diff --git a/drivers/net/dsa/microchip/ksz_common.c b/drivers/net/dsa/microchip/ksz_common.c
> index 1a9d6f83a0232..81798a9fa671d 100644
> --- a/drivers/net/dsa/microchip/ksz_common.c
> +++ b/drivers/net/dsa/microchip/ksz_common.c
> @@ -1486,6 +1486,41 @@ const struct ksz_chip_data ksz_switch_chips[] = {
>  		.gbit_capable	= {true, true, true, true, true, true, true},
>  	},
>  
> +	[KSZ9897S] = {
> +		.chip_id = KSZ9897S_CHIP_ID,
> +		.dev_name = "KSZ9897S",

[ ... ]

> +		.gbit_capable	= {true, true, true, true, true, true, true},
> +		.sgmii_port = 7,
> +	},
> +
>  	[KSZ9893] = {
>  		.chip_id = KSZ9893_CHIP_ID,
>  		.dev_name = "KSZ9893",

[ ... ]

> @@ -3933,7 +3969,30 @@ int ksz_switch_register(struct ksz_device *dev)
>  	if (ret)
>  		return ret;
>  
> -	info = ksz_lookup_info(dev->chip_id);
> +	lookup_chip_id = dev->chip_id;
> +

[ ... ]

> +	 * Only the chip_data entry differs, so dev->chip_id keeps the shared
> +	 * chip ID and nothing else has to know about the variant.
> +	 */
> +	if (dev->chip_id == KSZ9897_CHIP_ID) {
> +		u8 val;
> +
> +		ret = ksz_read8(dev, KSZ9897_REG_PORT7_XMII_CTRL_0, &val);
> +		if (ret)
> +			return ret;
> +
> +		if (val & KSZ9897_PORT7_SGMII_SEL)
> +			lookup_chip_id = KSZ9897S_CHIP_ID;
> +	}
> +
> +	info = ksz_lookup_info(lookup_chip_id);
>  	if (!info)
>  		return -ENODEV;
>  

> diff --git a/include/linux/platform_data/microchip-ksz.h b/include/linux/platform_data/microchip-ksz.h
> index 028781ad40593..fe8df1774289c 100644
> --- a/include/linux/platform_data/microchip-ksz.h
> +++ b/include/linux/platform_data/microchip-ksz.h
> @@ -34,6 +34,7 @@ enum ksz_chip_id {
>  	KSZ9477_CHIP_ID = 0x00947700,
>  	KSZ9896_CHIP_ID = 0x00989600,
>  	KSZ9897_CHIP_ID = 0x00989700,
> +	KSZ9897S_CHIP_ID = 0x00989701,
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

[Severity: Medium]
Is enum ksz_chip_id in include/linux/platform_data/microchip-ksz.h the right
place for this value, given that no code path can ever set dev->chip_id to
0x00989701?

ksz_switch_detect() masks off the revision byte and stores only the fixed
IDs, so a KSZ9897S always ends up with dev->chip_id == KSZ9897_CHIP_ID,
which the commit message describes as intentional:

    dev->chip_id keeps the KSZ9897 chip ID that both parts report

Because enum ksz_chip_id is the platform-data selection interface, a board
that sets ksz_platform_data.chip_id = KSZ9897S_CHIP_ID now reaches
ksz_check_device_id() with an expected ID that resolves through
ksz_lookup_info() but never matches the detected one:

drivers/net/dsa/microchip/ksz_common.c:ksz_check_device_id() {
	if (dev->pdata) {
		expected_chip_id = dev->pdata->chip_id;
		expected_chip_data = ksz_lookup_info(expected_chip_id);
		if (WARN_ON(!expected_chip_data))
			return -ENODEV;
	...
	if (expected_chip_id != dev->chip_id) {
		dev_err(dev->dev,
			"Device tree specifies chip %s but found %s, please fix it!\n",
			expected_chip_data->dev_name, dev->info->dev_name);
		return -ENODEV;
	}
}

Would such a board fail to probe with the confusing message "Device tree
specifies chip KSZ9897S but found KSZ9897, please fix it!"?

There is also the invariant question: every other entry in
ksz_switch_chips[] has a .chip_id equal to an ID the hardware can actually
report, and that value is consumed as a real chip ID elsewhere, for example
via dev->info->chip_id in lan937x_main.c. The new entry uses .chip_id purely
as a lookup key for ksz_lookup_info(lookup_chip_id) in
ksz_switch_register().

Would a private enum ksz_model index, or a bool in struct ksz_chip_data,
express the S/R variant without publishing an ID in the shared platform-data
header that no caller can use?

>  	KSZ9893_CHIP_ID = 0x00989300,
>  	KSZ9563_CHIP_ID = 0x00956300,
>  	KSZ8567_CHIP_ID = 0x00856700,

-- 
Sashiko AI review · https://netdev-ai.bots.linux.dev/sashiko/#/patchset/20260904-ksz9897-sgmii-port-v5-1-9bd4a0381aa8%40vaisala.com