drm/i915/display: Optimize panel power-on wait time

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@intel.com>
Link: https://lore.kernel.org/r/20250807082402.79018-1-dibin.moolakadan.subrahmanian@intel.com
Signed-off-by: Jani Nikula <jani.nikula@intel.com>

diff --git a/drivers/gpu/drm/i915/display/intel_pps.c b/drivers/gpu/drm/i915/display/intel_pps.c
index b64d0b30f5b12aa83b0cb05c81bb2acc19ce11c4..b84eb43bd2d01d1dabf4f7879b6999b11fee879c 100644 (file)
--- 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");
 }