Claude review: drm/panel: novatek-nt36672a: Convert to mipi_dsi_*_multi() helpers

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

Patch Review

**nt36672a_send_cmds conversion** - The switch from `mipi_dsi_dcs_write(pinfo->link, cmd->data[0], cmd->data + 1, 1)` to `mipi_dsi_dcs_write_buffer_multi(dsi_ctx, cmd->data, sizeof(cmd->data))` is semantically equivalent. Good.

**Behavioral change in unprepare error path** - This is the main concern. In the new code at lines 111-116:

```c
nt36672a_send_cmds(&dsi_ctx, pinfo->desc->off_cmds,
		   pinfo->desc->num_off_cmds);

mipi_dsi_dcs_set_display_off_multi(&dsi_ctx);
/* Reset error to continue power-down even if display off failed */
dsi_ctx.accum_err = 0;
```

If `nt36672a_send_cmds()` fails (setting `accum_err`), then `mipi_dsi_dcs_set_display_off_multi()` will be a no-op because all `_multi` helpers bail out early when `accum_err != 0`. The `accum_err = 0` reset comes *after* `set_display_off_multi`, so it doesn't help. In the original code, `set_display_off` was always attempted independently regardless of whether off_cmds succeeded. For a power-down path, you generally want to try everything. The reset should be moved *before* `set_display_off_multi`:

```c
nt36672a_send_cmds(&dsi_ctx, pinfo->desc->off_cmds,
		   pinfo->desc->num_off_cmds);

/* Reset error to continue power-down even if off cmds failed */
dsi_ctx.accum_err = 0;

mipi_dsi_dcs_set_display_off_multi(&dsi_ctx);
```

Or alternatively, reset `accum_err` both before `set_display_off_multi` and after it, to also handle its failure.

**120ms sleep uses plain `msleep()` instead of `mipi_dsi_msleep()`** (line 119) - This is actually correct behavior here, since the 120ms delay must always occur unconditionally during power-down regardless of prior errors. Good.

**nt36672a_panel_prepare error path** - The pattern of seeding `accum_err` from `nt36672a_panel_power_on()` at line 158 is a good use of the multi context:

```c
dsi_ctx.accum_err = nt36672a_panel_power_on(pinfo);
```

The error cleanup at lines 177-178 preserves the original behavior:

```c
if (dsi_ctx.accum_err < 0)
    gpiod_set_value(pinfo->reset_gpio, 0);
```

Note: the original `poweroff:` label also set the GPIO to 0, which appears to be a pre-existing issue (this de-asserts reset rather than re-asserting it, so it's effectively a no-op after a successful `power_on`). Not introduced by this patch.

**Lost error context** - The original code had specific `dev_err` messages like `"failed to send DCS off cmds: %d"` and `"set_display_off cmd failed ret = %d"`. These are all removed. While the low-level `_multi` helpers do log transport-level errors, the higher-level context (which operation was being attempted) is lost. This is typical for multi conversions and generally accepted, but worth noting.

**nt36672a_panel_power_off** - Dropping the error code from the log message (line 101-102):

```c
if (regulator_bulk_disable(ARRAY_SIZE(pinfo->supplies), pinfo->supplies) < 0)
    dev_err(panel->dev, "regulator_bulk_disable failed\n");
```

Minor nit: the original included `%d` with the error code, which can be useful for debugging. Consider preserving it:
```c
int ret = regulator_bulk_disable(...);
if (ret)
    dev_err(panel->dev, "regulator_bulk_disable failed %d\n", ret);
```

**Summary**: The conversion is mostly correct. The one issue that should be fixed before merging is the `accum_err` reset placement in `nt36672a_panel_unprepare()`, which causes `set_display_off` to be skipped when `send_cmds` fails. Move the reset before `set_display_off_multi()` to preserve the original always-try-everything power-down behavior.

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