[PATCH v2] drm/bridge: adv7511: Clear HPD IRQ during atomic_enable()

[Biju]

From: Biju Das <biju.das.jz@xxxxxxxxxxxxxx>

On RZ/G3E SMARC EVK, suspend-to-RAM via PSCI powers down the ADV7535
chip entirely, causing the HPD status bit to be in a stale state on
resume. When the display controller driver's system PM resume callback
invokes drm_mode_config_helper_resume(), it calls the bridge's
atomic_enable(), but the stale HPD IRQ is never cleared, leading to
incorrect behaviour.

Clear the HPD status bit in adv7511_bridge_atomic_enable() after
powering on, so that any HPD interrupt latched before or during
power-loss is dismissed before normal operation resumes.

Signed-off-by: Biju Das <biju.das.jz@xxxxxxxxxxxxxx>
---
Tested HPD, s2idle and s2ram on RZ/G3L SMARC EVK connected to ADV7535
on both polling and IRQ mode.
v1->v2:
 * Dropped PM support instead clearing latched HPD status bit in
   adv7511_bridge_atomic_enable()
 * Dropped suspended variable from struct adv7511.
 * Updated comment in adv7511_bridge_atomic_enable().
 * Clearing the HPD status bit unconditionally as there is no harm.
 * Updated commit header and description.
 * Dropped the tags.
---
 drivers/gpu/drm/bridge/adv7511/adv7511_drv.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/gpu/drm/bridge/adv7511/adv7511_drv.c b/drivers/gpu/drm/bridge/adv7511/adv7511_drv.c
index 6bd76c1fb007..7663814b4032 100644
--- a/drivers/gpu/drm/bridge/adv7511/adv7511_drv.c
+++ b/drivers/gpu/drm/bridge/adv7511/adv7511_drv.c
@@ -792,6 +792,13 @@ static void adv7511_bridge_atomic_enable(struct drm_bridge *bridge,
 
 	adv7511_power_on(adv);
 
+	/*
+	 * Clear the HPD status bit (ADV7511_INT0_HPD), so that any HPD
+	 * interrupt latched before or during power loss is dismissed before
+	 * normal operation resumes.
+	 */
+	regmap_write(adv->regmap, ADV7511_REG_INT(0), ADV7511_INT0_HPD);
+
 	connector = drm_atomic_get_new_connector_for_encoder(state, bridge->encoder);
 	if (WARN_ON(!connector))
 		return;
-- 
2.43.0