drm/i915: Treat crtc->mode.clock == 0 as disabled

Prevent a divide-by-zero by consistently treating an 'active' CRTC
without a mode set as actually disabled.

This looks to have been first introduced with

commit 24929352481f085c5f85d4d4cbc919ddf106d381
Author: Daniel Vetter <daniel.vetter@ffwll.ch>
Date:   Mon Jul 2 20:28:59 2012 +0200

    drm/i915: read out the modeset hw state at load and resume time

but then combined with

commit b0a2658acb5bf9ca86b4aab011b7106de3af0add
Author: Daniel Vetter <daniel.vetter@ffwll.ch>
Date:   Tue Dec 18 09:37:54 2012 +0100

    drm/i915: don't disable disconnected outputs

it finally started oopsing.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reported-and-tested-by: Alexey Zaytsev <alexey.zaytsev@gmail.com>
Tested-by: Sedat Dilek <sedat.dilek@gmail.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Jesse Barnes <jbarnes@virtuousgeek.org>
Cc: stable@vger.kernel.org
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

1 files changed, 16 insertions, 9 deletions

diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
index e6f54ffab3ba..e83a11794172 100644
--- a/drivers/gpu/drm/i915/intel_pm.c
+++ b/drivers/gpu/drm/i915/intel_pm.c
@@ -44,6 +44,14 @@
  * i915.i915_enable_fbc parameter
  */
 
+static bool intel_crtc_active(struct drm_crtc *crtc)
+{
+        /* Be paranoid as we can arrive here with only partial
+         * state retrieved from the hardware during setup.
+         */
+        return to_intel_crtc(crtc)->active && crtc->fb && crtc->mode.clock;
+}
+
 static void i8xx_disable_fbc(struct drm_device *dev)
 {
         struct drm_i915_private *dev_priv = dev->dev_private;
@@ -405,9 +413,8 @@ void intel_update_fbc(struct drm_device *dev)
          *   - going to an unsupported config (interlace, pixel multiply, etc.)
          */
         list_for_each_entry(tmp_crtc, &dev->mode_config.crtc_list, head) {
-                if (to_intel_crtc(tmp_crtc)->active &&
-                    !to_intel_crtc(tmp_crtc)->primary_disabled &&
-                    tmp_crtc->fb) {
+                if (intel_crtc_active(tmp_crtc) &&
+                    !to_intel_crtc(tmp_crtc)->primary_disabled) {
                         if (crtc) {
                                 DRM_DEBUG_KMS("more than one pipe active, disabling compression\n");
                                 dev_priv->no_fbc_reason = FBC_MULTIPLE_PIPES;
@@ -992,7 +999,7 @@ static struct drm_crtc *single_enabled_crtc(struct drm_device *dev)
         struct drm_crtc *crtc, *enabled = NULL;
 
         list_for_each_entry(crtc, &dev->mode_config.crtc_list, head) {
-                if (to_intel_crtc(crtc)->active && crtc->fb) {
+                if (intel_crtc_active(crtc)) {
                         if (enabled)
                                 return NULL;
                         enabled = crtc;
@@ -1086,7 +1093,7 @@ static bool g4x_compute_wm0(struct drm_device *dev,
         int entries, tlb_miss;
 
         crtc = intel_get_crtc_for_plane(dev, plane);
-        if (crtc->fb == NULL || !to_intel_crtc(crtc)->active) {
+        if (!intel_crtc_active(crtc)) {
                 *cursor_wm = cursor->guard_size;
                 *plane_wm = display->guard_size;
                 return false;
@@ -1215,7 +1222,7 @@ static bool vlv_compute_drain_latency(struct drm_device *dev,
         int entries;
 
         crtc = intel_get_crtc_for_plane(dev, plane);
-        if (crtc->fb == NULL || !to_intel_crtc(crtc)->active)
+        if (!intel_crtc_active(crtc))
                 return false;
 
         clock = crtc->mode.clock;       /* VESA DOT Clock */
@@ -1476,7 +1483,7 @@ static void i9xx_update_wm(struct drm_device *dev)
 
         fifo_size = dev_priv->display.get_fifo_size(dev, 0);
         crtc = intel_get_crtc_for_plane(dev, 0);
-        if (to_intel_crtc(crtc)->active && crtc->fb) {
+        if (intel_crtc_active(crtc)) {
                 int cpp = crtc->fb->bits_per_pixel / 8;
                 if (IS_GEN2(dev))
                         cpp = 4;
@@ -1490,7 +1497,7 @@ static void i9xx_update_wm(struct drm_device *dev)
 
         fifo_size = dev_priv->display.get_fifo_size(dev, 1);
         crtc = intel_get_crtc_for_plane(dev, 1);
-        if (to_intel_crtc(crtc)->active && crtc->fb) {
+        if (intel_crtc_active(crtc)) {
                 int cpp = crtc->fb->bits_per_pixel / 8;
                 if (IS_GEN2(dev))
                         cpp = 4;
@@ -2044,7 +2051,7 @@ sandybridge_compute_sprite_wm(struct drm_device *dev, int plane,
         int entries, tlb_miss;
 
         crtc = intel_get_crtc_for_plane(dev, plane);
-        if (crtc->fb == NULL || !to_intel_crtc(crtc)->active) {
+        if (!intel_crtc_active(crtc)) {
                 *sprite_wm = display->guard_size;
                 return false;
         }