Re: [PATCH 3/4] platform/chrome: cros_ec_typec: Configure muxes at start of port update

Tzung-Bi Shih
2022-02-08T05:39:43Z

On Mon, Feb 07, 2022 at 09:40:28PM +0000, Prashant Malani wrote:
> There are situations where the mux state reported by the Embedded
> Controller (EC), might lag the partner "connected" state. So, the mux
> state might still suggest that a partner is connected, while the PD
> "connected" state, being in Try.SNK (for example) suggests that the
> partner is disconnected.
>
> In such a scenario, we will end up sending a disconnect command to the
> mux driver, followed by a connect command, since the mux is configured
> later. Avoid this by configuring the mux before
> registering/disconnecting a partner.

I failed to understand the description. It looks like some protocol details.
Could you provide some brief explanation in the commit message?

On a related note, followed up the example scenario, which one of the
understanding is the most applicable:
1) The disconnect followed by a connect is suboptimal. The patch cleans it.
2) The disconnect followed by a connect is a bug. The patch fixes it.

> @@ -965,6 +965,11 @@ static int cros_typec_port_update(struct cros_typec_data *typec, int port_num)
> if (ret < 0)
> return ret;
>
> + /* Update the switches if they exist, according to requested state */
> + ret = cros_typec_configure_mux(typec, port_num, &resp);
> + if (ret)
> + dev_warn(typec->dev, "Configure muxes failed, err = %d\n", ret);

It used the fact that the function returns `ret` at the end. After the move,
the block is no longer the last thing before function returns.

Does it make more sense to return earlier if cros_typec_configure_mux() fails?
Does the rest of code need to be executed even if cros_typec_configure_mux()
fails?

> @@ -980,11 +985,6 @@ static int cros_typec_port_update(struct cros_typec_data *typec, int port_num)
> if (typec->typec_cmd_supported)
> cros_typec_handle_status(typec, port_num);
>
> - /* Update the switches if they exist, according to requested state */
> - ret = cros_typec_configure_mux(typec, port_num, &resp);
> - if (ret)
> - dev_warn(typec->dev, "Configure muxes failed, err = %d\n", ret);
> -
> return ret;

If the function decides to return earlier, it can be `return 0;`.