[PATCH] drm: renesas: shmobile: Call drm_helper_force_disable_all() at shutdown time

[Geert Uytterhoeven <geert+renesas@glider.be>]

From: Douglas Anderson <dianders@chromium.org>

Based on grepping through the source code, this driver appears to be
missing a call to drm_atomic_helper_shutdown() at system shutdown time.
This is important because drm_helper_force_disable_all() will cause
panels to get disabled cleanly which may be important for their power
sequencing.  Future changes will remove any custom powering off in
individual panel drivers so the DRM drivers need to start getting this
right.

The fact that we should call drm_atomic_helper_shutdown() in the case of
OS shutdown comes straight out of the kernel doc "driver instance
overview" in drm_drv.c.

Suggested-by: Maxime Ripard <mripard@kernel.org>
Signed-off-by: Douglas Anderson <dianders@chromium.org>
Link: https://lore.kernel.org/r/20230901164111.RFT.15.Iaf638a1d4c8b3c307a6192efabb4cbb06b195f15@changeid
[geert: s/drm_helper_force_disable_all/drm_atomic_helper_shutdown/]
[geert: shmob_drm_remove() already calls drm_atomic_helper_shutdown]
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
---
Tested on Atmark Techno Armadillo-800-EVA, where the PWM instance
driving the backlight is now stopped on shutdown.
Panel-simple does print two new warnings:

    +panel-simple panel: Skipping disable of already disabled panel
    +panel-simple panel: Skipping unprepare of already unprepared panel
     reboot: System halted
---
 drivers/gpu/drm/renesas/shmobile/shmob_drm_drv.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/drivers/gpu/drm/renesas/shmobile/shmob_drm_drv.c b/drivers/gpu/drm/renesas/shmobile/shmob_drm_drv.c
index bd16d4780c6436c3..a15162be26f259a4 100644
--- a/drivers/gpu/drm/renesas/shmobile/shmob_drm_drv.c
+++ b/drivers/gpu/drm/renesas/shmobile/shmob_drm_drv.c
@@ -171,6 +171,13 @@ static void shmob_drm_remove(struct platform_device *pdev)
 	drm_kms_helper_poll_fini(ddev);
 }
 
+static void shmob_drm_shutdown(struct platform_device *pdev)
+{
+	struct shmob_drm_device *sdev = platform_get_drvdata(pdev);
+
+	drm_atomic_helper_shutdown(&sdev->ddev);
+}
+
 static int shmob_drm_probe(struct platform_device *pdev)
 {
 	struct shmob_drm_platform_data *pdata = pdev->dev.platform_data;
@@ -274,6 +281,7 @@ static const struct of_device_id shmob_drm_of_table[] __maybe_unused = {
 static struct platform_driver shmob_drm_platform_driver = {
 	.probe		= shmob_drm_probe,
 	.remove_new	= shmob_drm_remove,
+	.shutdown	= shmob_drm_shutdown,
 	.driver		= {
 		.name	= "shmob-drm",
 		.of_match_table = of_match_ptr(shmob_drm_of_table),
-- 
2.34.1