[Intel-gfx] [PATCHv2] drm/i915/dp: Change aux_ctl reg read to polling read

[Arun R Murthy]

The busy timeout logic checks for the AUX BUSY, then waits for the
timeout period and then after timeout reads the register for BUSY set
and fails.
Instead replace interrupt with polling so as to read the AUX CTL
register often before the timeout period.

v2: replace interrupt with polling read

Signed-off-by: Arun R Murthy <arun.r.mur...@intel.com>
---
 drivers/gpu/drm/i915/display/intel_dp_aux.c | 24 ++++++++++++---------
 1 file changed, 14 insertions(+), 10 deletions(-)

diff --git a/drivers/gpu/drm/i915/display/intel_dp_aux.c 
b/drivers/gpu/drm/i915/display/intel_dp_aux.c
index 664bebdecea7..22c0a59850df 100644
--- a/drivers/gpu/drm/i915/display/intel_dp_aux.c
+++ b/drivers/gpu/drm/i915/display/intel_dp_aux.c
@@ -40,20 +40,24 @@ intel_dp_aux_wait_done(struct intel_dp *intel_dp)
        i915_reg_t ch_ctl = intel_dp->aux_ch_ctl_reg(intel_dp);
        const unsigned int timeout_ms = 10;
        u32 status;
-       bool done;
-
-#define C (((status = intel_uncore_read_notrace(&i915->uncore, ch_ctl)) & 
DP_AUX_CH_CTL_SEND_BUSY) == 0)
-       done = wait_event_timeout(i915->display.gmbus.wait_queue, C,
-                                 msecs_to_jiffies_timeout(timeout_ms));
+       int try;
 
+       for (try = 0; try < 10; try++) {
+               status = intel_uncore_read_notrace(&i915->uncore, ch_ctl);
+               if ((status & DP_AUX_CH_CTL_SEND_BUSY) == 0)
+                       break;
+               msleep(1);
+       }
        /* just trace the final value */
        trace_i915_reg_rw(false, ch_ctl, status, sizeof(status), true);
 
-       if (!done)
-               drm_err(&i915->drm,
-                       "%s: did not complete or timeout within %ums (status 
0x%08x)\n",
-                       intel_dp->aux.name, timeout_ms, status);
-#undef C
+       if (try == 3) {
+               status = intel_uncore_read_notrace(&i915->uncore, ch_ctl);
+               if ((status & DP_AUX_CH_CTL_SEND_BUSY) != 0)
+                       drm_err(&i915->drm,
+                               "%s: did not complete or timeout within %ums 
(status 0x%08x)\n",
+                               intel_dp->aux.name, timeout_ms, status);
+       }
 
        return status;
 }
-- 
2.25.1