[PATCH v2] HID: i2c-hid: Unfollow the panel on shutdown

[Justin Yeh <justin.yeh@mediatek.com>]

i2c_hid_core_shutdown() sends SET_POWER(SLEEP) even for panel followers,
but nothing in device_shutdown() guarantees whether the panel, and hence
our own power, is still on by the time we get there.

Do what i2c_hid_core_remove() does and just unfollow the panel.
drm_panel_remove_follower() calls panel_unpreparing() only while the
panel is still prepared, which powers us down properly; if it is already
unprepared no transfer is attempted at all. On MT8196 the panel is
unprepared long before us, so this also drops the ~2s i2c bus timeout
from every reboot.

Fixes: 96a37bfd232a ("HID: i2c-hid: Support being a panel follower")
Suggested-by: Douglas Anderson <dianders@chromium.org>
Signed-off-by: Justin Yeh <justin.yeh@mediatek.com>
---
Changes in v2:
- Unfollow the panel instead of just skipping SET_POWER, so we no longer
  depend on the panel having been unprepared before us (Doug).
- Link to v1: https://lore.kernel.org/all/20260904035009.4114363-1-justin.yeh@mediatek.com/
---
 drivers/hid/i2c-hid/i2c-hid-core.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/drivers/hid/i2c-hid/i2c-hid-core.c b/drivers/hid/i2c-hid/i2c-hid-core.c
index 0ff07fdab442..c7e46004f513 100644
--- a/drivers/hid/i2c-hid/i2c-hid-core.c
+++ b/drivers/hid/i2c-hid/i2c-hid-core.c
@@ -1355,7 +1355,16 @@ void i2c_hid_core_shutdown(struct i2c_client *client)
 {
 	struct i2c_hid *ihid = i2c_get_clientdata(client);
 
-	i2c_hid_set_power(ihid, I2C_HID_PWR_SLEEP);
+	/*
+	 * Like in i2c_hid_core_remove(): if we're a follower, the act of
+	 * unfollowing will cause us to be powered down. Otherwise we need to
+	 * manually do it.
+	 */
+	if (ihid->is_panel_follower)
+		drm_panel_remove_follower(&ihid->panel_follower);
+	else
+		i2c_hid_set_power(ihid, I2C_HID_PWR_SLEEP);
+
 	free_irq(client->irq, ihid);
 
 	i2c_hid_core_shutdown_tail(ihid);
-- 
2.45.2