[Intel-gfx] [PATCH] drm/i915/display: Reset message bus after each read/write operation

[Mika Kahola]

Every know and then we receive the following error when running
for example IGT test kms_flip.

[drm] *ERROR* PHY G Read 0d80 failed after 3 retries.
[drm] *ERROR* PHY G Write 0d81 failed after 3 retries.

Since the error is sporadic in nature, the patch proposes
to reset the message bus after every successful or unsuccessful
read or write operation. However, testing revealed that this
alone is not sufficient method an additiona delay is also
introduces anything from 200us to 300us. This delay is experimental
value and has no specification to back it up.

Signed-off-by: Mika Kahola <mika.kah...@intel.com>
---
 drivers/gpu/drm/i915/display/intel_cx0_phy.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/gpu/drm/i915/display/intel_cx0_phy.c 
b/drivers/gpu/drm/i915/display/intel_cx0_phy.c
index abd607b564f1..a71b8a29d6b0 100644
--- a/drivers/gpu/drm/i915/display/intel_cx0_phy.c
+++ b/drivers/gpu/drm/i915/display/intel_cx0_phy.c
@@ -220,9 +220,12 @@ static u8 __intel_cx0_read(struct drm_i915_private *i915, 
enum port port,
        /* 3 tries is assumed to be enough to read successfully */
        for (i = 0; i < 3; i++) {
                status = __intel_cx0_read_once(i915, port, lane, addr);
+               intel_cx0_bus_reset(i915, port, lane);
 
                if (status >= 0)
                        return status;
+
+               usleep_range(200, 300);
        }
 
        drm_err_once(&i915->drm, "PHY %c Read %04x failed after %d retries.\n",
@@ -299,9 +302,12 @@ static void __intel_cx0_write(struct drm_i915_private 
*i915, enum port port,
        /* 3 tries is assumed to be enough to write successfully */
        for (i = 0; i < 3; i++) {
                status = __intel_cx0_write_once(i915, port, lane, addr, data, 
committed);
+               intel_cx0_bus_reset(i915, port, lane);
 
                if (status == 0)
                        return;
+
+               usleep_range(200, 300);
        }
 
        drm_err_once(&i915->drm,
-- 
2.34.1