Claude review: drm/display/dp: Export function to wake the sink AUX_CH

[Claude Code Review Bot <claude-review@example.com>]

Patch Review

**`poll_timeout_us` misuse:**

```c
ret = poll_timeout_us(ret = drm_dp_dpcd_readb(aux, DP_SET_POWER, &value),
                      ret > 0,
                      1000, wake_retry * 1000, true);
```

The variable `ret` is used both as the operation result (inside the macro expansion) AND as the macro's return value. After the macro completes, `ret` holds the macro's return value (0 or `-ETIMEDOUT`), not the `drm_dp_dpcd_readb` return value. This means the `ret < 0` check below is only checking for `-ETIMEDOUT` from the poll, not a DPCD read failure. This is confusing and fragile — use a separate variable for the poll result.

**Condition logic concern:**

```c
if (value == DP_SET_POWER_D3 || ret < 0) {
```

If the poll times out (ret == -ETIMEDOUT), `value` might contain stale or partial data from a failed read. The function proceeds to write to `DP_SET_POWER` without checking whether DPCD writes actually succeed — no error checking on either `drm_dp_dpcd_writeb` call.

**Wake sequence concern:**

```c
drm_dp_dpcd_writeb(aux, DP_SET_POWER, DP_SET_POWER_D0);
fsleep(1000);
drm_dp_dpcd_writeb(aux, DP_SET_POWER, DP_SET_POWER_D3_AUX_ON);
```

Setting to D0 and then immediately to D3_AUX_ON seems odd. The cover letter and spec reference (Section 2.3.4) say the goal is to wake the sink for AUX communication, but D3_AUX_ON is still a low-power state. If the caller is about to retry an AUX transaction, why not leave it in D0? The intent should be clarified.

**Missing `#include`:** The function uses `poll_timeout_us` from `<linux/iopoll.h>` and `fsleep`. Ensure the drm_dp_helper.c file includes the necessary headers.

**Naming:** `drm_dp_wake_sink` is generic but it specifically deals with AUX channel power states. A name like `drm_dp_aux_wake_sink` might be more precise.

**Documentation:** The kerneldoc is incomplete — it should describe the behavior (what it does on success/failure, return value semantics — though it's void).

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