[SRU][Questing][PATCH 1/8] drm/i915/display: Optimize panel power-on wait time

[You-Sheng Yang]

From: Dibin Moolakadan Subrahmanian <dibin.moolakadan.subrahmanian at intel.com>

BugLink: https://bugs.launchpad.net/bugs/2137272

The current wait_panel_status() uses intel_de_wait(),
which internally on Xe platforms calls  xe_mmio_wait32().
xe_mmio_wait32() increases poll interval exponentially.

This exponential poll interval increase causes unnessory delays
during resume or power-on when the panel becomes ready earlier,
but polling is delayed due to backoff.

Replace intel_de_wait() with read_poll_timeout() +
intel_de_read() to actively poll the register at a fixed 10ms interval
up to a 5 second timeout. This allows poll to exit
early  when panel is ready.

Changes in v2:
Replaced  two-phase intel_de_wait() with  read_poll_timeout()
 + intel_de_read()
Changes in v3:
 - Add poll_interval_ms argument  'wait_panel_status' function.
 - Modify 'wait_panel_status' callers with proper poll interval
Changes in v4:
 - Change 'wait_panel_off' poll interval to 10ms
Changes in v5:
 - Dropped  poll_interval_ms parameter,use fixed polling
   interval of 10ms (Jani Nikula)
Changes in v6:
 - Removed goto in error path

Signed-off-by: Dibin Moolakadan Subrahmanian <dibin.moolakadan.subrahmanian at intel.com>
Link: https://lore.kernel.org/r/20250807082402.79018-1-dibin.moolakadan.subrahmanian@intel.com
Signed-off-by: Jani Nikula <jani.nikula at intel.com>
(cherry picked from commit 1ebc27248ea0b81f0023ca28894ac40183b86b7c)
Signed-off-by: You-Sheng Yang <vicamo.yang at canonical.com>
---
 drivers/gpu/drm/i915/display/intel_pps.c | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/display/intel_pps.c b/drivers/gpu/drm/i915/display/intel_pps.c
index b64d0b30f5b12..b84eb43bd2d01 100644
--- a/drivers/gpu/drm/i915/display/intel_pps.c
+++ b/drivers/gpu/drm/i915/display/intel_pps.c
@@ -4,6 +4,7 @@
  */
 
 #include <linux/debugfs.h>
+#include <linux/iopoll.h>
 
 #include <drm/drm_print.h>
 
@@ -608,6 +609,8 @@ static void wait_panel_status(struct intel_dp *intel_dp,
 	struct intel_display *display = to_intel_display(intel_dp);
 	struct intel_digital_port *dig_port = dp_to_dig_port(intel_dp);
 	i915_reg_t pp_stat_reg, pp_ctrl_reg;
+	int ret;
+	u32 val;
 
 	lockdep_assert_held(&display->pps.mutex);
 
@@ -624,13 +627,20 @@ static void wait_panel_status(struct intel_dp *intel_dp,
 		    intel_de_read(display, pp_stat_reg),
 		    intel_de_read(display, pp_ctrl_reg));
 
-	if (intel_de_wait(display, pp_stat_reg, mask, value, 5000))
+	ret = read_poll_timeout(intel_de_read, val,
+				(val & mask) == value,
+				10 * 1000, 5000 * 1000, true,
+				display, pp_stat_reg);
+
+	if (ret) {
 		drm_err(display->drm,
 			"[ENCODER:%d:%s] %s panel status timeout: PP_STATUS: 0x%08x PP_CONTROL: 0x%08x\n",
 			dig_port->base.base.base.id, dig_port->base.base.name,
 			pps_name(intel_dp),
 			intel_de_read(display, pp_stat_reg),
 			intel_de_read(display, pp_ctrl_reg));
+		return;
+	}
 
 	drm_dbg_kms(display->drm, "Wait complete\n");
 }
-- 
2.51.0