drm/i915: Retry reading the PCH FDI receiver ISR

According to the PRM (Vol3P2), the PCH FDI receiver ISR read for bit lock
should be retried at least once. This patch retries the read 5 times
with a small delay in between reads. I've had reports of display corruption
on resume with "FDI train 1 fail!", so I'm hoping that adding this retry
will mitigate the issue.

Signed-off-by: Sean Paul <seanpaul@chromium.org>
Reviewed-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index de1ba19726f7de28e700592c1fbdff47d02dbe92..615b3973114b894a2d2050bc97ad50077522bbda 100644 (file)
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -2537,7 +2537,7 @@ static void gen6_fdi_link_train(struct drm_crtc *crtc)
        struct drm_i915_private *dev_priv = dev->dev_private;
        struct intel_crtc *intel_crtc = to_intel_crtc(crtc);
        int pipe = intel_crtc->pipe;
-       u32 reg, temp, i;
+       u32 reg, temp, i, retry;
 
        /* Train 1: umask FDI RX Interrupt symbol_lock and bit_lock bit
           for train result */
@@ -2589,15 +2589,19 @@ static void gen6_fdi_link_train(struct drm_crtc *crtc)
                POSTING_READ(reg);
                udelay(500);
 
-               reg = FDI_RX_IIR(pipe);
-               temp = I915_READ(reg);
-               DRM_DEBUG_KMS("FDI_RX_IIR 0x%x\n", temp);
-
-               if (temp & FDI_RX_BIT_LOCK) {
-                       I915_WRITE(reg, temp | FDI_RX_BIT_LOCK);
-                       DRM_DEBUG_KMS("FDI train 1 done.\n");
-                       break;
+               for (retry = 0; retry < 5; retry++) {
+                       reg = FDI_RX_IIR(pipe);
+                       temp = I915_READ(reg);
+                       DRM_DEBUG_KMS("FDI_RX_IIR 0x%x\n", temp);
+                       if (temp & FDI_RX_BIT_LOCK) {
+                               I915_WRITE(reg, temp | FDI_RX_BIT_LOCK);
+                               DRM_DEBUG_KMS("FDI train 1 done.\n");
+                               break;
+                       }
+                       udelay(50);
                }
+               if (retry < 5)
+                       break;
        }
        if (i == 4)
                DRM_ERROR("FDI train 1 fail!\n");
@@ -2638,15 +2642,19 @@ static void gen6_fdi_link_train(struct drm_crtc *crtc)
                POSTING_READ(reg);
                udelay(500);
 
-               reg = FDI_RX_IIR(pipe);
-               temp = I915_READ(reg);
-               DRM_DEBUG_KMS("FDI_RX_IIR 0x%x\n", temp);
-
-               if (temp & FDI_RX_SYMBOL_LOCK) {
-                       I915_WRITE(reg, temp | FDI_RX_SYMBOL_LOCK);
-                       DRM_DEBUG_KMS("FDI train 2 done.\n");
-                       break;
+               for (retry = 0; retry < 5; retry++) {
+                       reg = FDI_RX_IIR(pipe);
+                       temp = I915_READ(reg);
+                       DRM_DEBUG_KMS("FDI_RX_IIR 0x%x\n", temp);
+                       if (temp & FDI_RX_SYMBOL_LOCK) {
+                               I915_WRITE(reg, temp | FDI_RX_SYMBOL_LOCK);
+                               DRM_DEBUG_KMS("FDI train 2 done.\n");
+                               break;
+                       }
+                       udelay(50);
                }
+               if (retry < 5)
+                       break;
        }
        if (i == 4)
                DRM_ERROR("FDI train 2 fail!\n");