Re: [PATCH net-next v1] net:dsa:yt922x: Add support for Motorcomm YT922x

[David Yang]

On Mon, Aug 17, 2026 at 6:40 PM Kyle Switch <kyle.switch@xxxxxxxxxxxxxx> wrote:
> >> +static int yt922x_cpu_tag_mode_set(struct yt921x_priv *priv)
> >> +{
> >> +       struct device *dev = to_device(priv);
> >> +       u16 eth_p_tag;
> >> +       u32 val;
> >> +       u32 val1;
> >> +       int res;
> >> +
> >> +       /* cpu tag mode set */
> >> +       res = yt921x_reg_read(priv, YT922X_CPU_TAG_RX_CTRL, &val);
> >> +       if (res)
> >> +               return res;
> >> +       res = yt921x_reg_read(priv, YT922X_CPU_TAG_TX_CTRL, &val1);
> >> +       if (res)
> >> +               return res;
> >> +       val &= ~YT922X_CPU_TAG_RX_MODE;
> >> +       val1 &= ~YT922X_CPU_TAG_TX_MODE;
> >> +       val1 &= ~YT922X_CPU_TAG_TX_TYPE;
> >> +       res = yt921x_reg_write(priv, YT922X_CPU_TAG_RX_CTRL, val);
> >> +       if (res)
> >> +               return res;
> >> +       res = yt921x_reg_write(priv, YT922X_CPU_TAG_TX_CTRL, val1);
> >> +       if (res)
> >> +               return res;
> >> +
> >> +       /* tpid check */
> >> +       res = yt921x_reg_read(priv, YT921X_CPU_TAG_TPID, &val);
> >> +       if (res)
> >> +               return res;
> >> +       eth_p_tag = FIELD_GET(YT921X_CPU_TAG_TPID_TPID_M, val);
> >> +       if (eth_p_tag != ETH_P_YT921X) {
> >> +               dev_err(dev, "Tag type 0x%x != 0x%x\n", eth_p_tag,
> >> +                       ETH_P_YT921X);
> >> +               return -EINVAL;
> >> +       }
> >> +
> >> +       return 0;
> >> +}
> > This looks similar to yt921x_chip_reset(), so you'd better merge it
> > into yt922x_chip_reset() above.
>
> Ans:Given that this interface is responsible for mode selection related
> to CPU tags, the cpu tag
>
>         TPID check has been consolidated here as well.

TPID does not depend on the tag mode, so this is a one-time validation
right after resetting in yt921x_chip_reset().

Also the naming is confusing: why `mode_set` clears the `RX/TX_MODE`.
It would be self-explanatory to rename it to `set_8b` and
`RX/TX_TAG_4B`, and/or mention the existence of 4b mode in the comment
for tag_yt922x as well.