drm/i915: Fix locking for intel_enable_pipe_a()

intel_enable_pipe_a() gets called with all the modeset locks already
held (by drm_modeset_lock_all()), so trying to grab the same
locks using another drm_modeset_acquire_ctx is going to fail miserably.

Move most of the drm_modeset_acquire_ctx handling (init/drop/fini)
out from intel_{get,release}_load_detect_pipe() into the callers
(intel_{crt,tv}_detect()). Only the actual locking and backoff
handling is left in intel_get_load_detect_pipe(). And in
intel_enable_pipe_a() we just share the mode_config.acquire_ctx from
drm_modeset_lock_all() which is already holding all the relevant locks.

It's perfectly legal to lock the same ww_mutex multiple times using the
same ww_acquire_ctx. drm_modeset_lock() will convert the returned
-EALREADY into 0, so the caller doesn't need to do antyhing special.

Fixes a hang on resume on my 830.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: stable@vger.kernel.org
Signed-off-by: Jani Nikula <jani.nikula@intel.com>

4 files changed, 17 insertions, 21 deletions

diff --git a/drivers/gpu/drm/i915/intel_crt.c b/drivers/gpu/drm/i915/intel_crt.c
index 2efaf8e8d9c4..e8abfce40976 100644
--- a/drivers/gpu/drm/i915/intel_crt.c
+++ b/drivers/gpu/drm/i915/intel_crt.c
@@ -699,16 +699,21 @@ intel_crt_detect(struct drm_connector *connector, bool force)
                 goto out;
         }
 
+        drm_modeset_acquire_init(&ctx, 0);
+
         /* for pre-945g platforms use load detect */
         if (intel_get_load_detect_pipe(connector, NULL, &tmp, &ctx)) {
                 if (intel_crt_detect_ddc(connector))
                         status = connector_status_connected;
                 else
                         status = intel_crt_load_detect(crt);
-                intel_release_load_detect_pipe(connector, &tmp, &ctx);
+                intel_release_load_detect_pipe(connector, &tmp);
         } else
                 status = connector_status_unknown;
 
+        drm_modeset_drop_locks(&ctx);
+        drm_modeset_acquire_fini(&ctx);
+
 out:
         intel_display_power_put(dev_priv, power_domain);
         return status;
diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index 018fb7222f60..f02c80d4039c 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -8462,8 +8462,6 @@ bool intel_get_load_detect_pipe(struct drm_connector *connector,
                       connector->base.id, connector->name,
                       encoder->base.id, encoder->name);
 
-        drm_modeset_acquire_init(ctx, 0);
-
 retry:
         ret = drm_modeset_lock(&config->connection_mutex, ctx);
         if (ret)
@@ -8574,15 +8572,11 @@ fail_unlock:
                 goto retry;
         }
 
-        drm_modeset_drop_locks(ctx);
-        drm_modeset_acquire_fini(ctx);
-
         return false;
 }
 
 void intel_release_load_detect_pipe(struct drm_connector *connector,
-                                    struct intel_load_detect_pipe *old,
-                                    struct drm_modeset_acquire_ctx *ctx)
+                                    struct intel_load_detect_pipe *old)
 {
         struct intel_encoder *intel_encoder =
                 intel_attached_encoder(connector);
@@ -8606,17 +8600,12 @@ void intel_release_load_detect_pipe(struct drm_connector *connector,
                         drm_framebuffer_unreference(old->release_fb);
                 }
 
-                goto unlock;
                 return;
         }
 
         /* Switch crtc and encoder back off if necessary */
         if (old->dpms_mode != DRM_MODE_DPMS_ON)
                 connector->funcs->dpms(connector, old->dpms_mode);
-
-unlock:
-        drm_modeset_drop_locks(ctx);
-        drm_modeset_acquire_fini(ctx);
 }
 
 static int i9xx_pll_refclk(struct drm_device *dev,
@@ -12659,7 +12648,7 @@ static void intel_enable_pipe_a(struct drm_device *dev)
         struct intel_connector *connector;
         struct drm_connector *crt = NULL;
         struct intel_load_detect_pipe load_detect_temp;
-        struct drm_modeset_acquire_ctx ctx;
+        struct drm_modeset_acquire_ctx *ctx = dev->mode_config.acquire_ctx;
 
         /* We can't just switch on the pipe A, we need to set things up with a
          * proper mode and output configuration. As a gross hack, enable pipe A
@@ -12676,10 +12665,8 @@ static void intel_enable_pipe_a(struct drm_device *dev)
         if (!crt)
                 return;
 
-        if (intel_get_load_detect_pipe(crt, NULL, &load_detect_temp, &ctx))
-                intel_release_load_detect_pipe(crt, &load_detect_temp, &ctx);
-
-
+        if (intel_get_load_detect_pipe(crt, NULL, &load_detect_temp, ctx))
+                intel_release_load_detect_pipe(crt, &load_detect_temp);
 }
 
 static bool
diff --git a/drivers/gpu/drm/i915/intel_drv.h b/drivers/gpu/drm/i915/intel_drv.h
index 4b2664bd5b81..fe3431f96900 100644
--- a/drivers/gpu/drm/i915/intel_drv.h
+++ b/drivers/gpu/drm/i915/intel_drv.h
@@ -830,8 +830,7 @@ bool intel_get_load_detect_pipe(struct drm_connector *connector,
                                 struct intel_load_detect_pipe *old,
                                 struct drm_modeset_acquire_ctx *ctx);
 void intel_release_load_detect_pipe(struct drm_connector *connector,
-                                    struct intel_load_detect_pipe *old,
-                                    struct drm_modeset_acquire_ctx *ctx);
+                                    struct intel_load_detect_pipe *old);
 int intel_pin_and_fence_fb_obj(struct drm_device *dev,
                                struct drm_i915_gem_object *obj,
                                struct intel_engine_cs *pipelined);
diff --git a/drivers/gpu/drm/i915/intel_tv.c b/drivers/gpu/drm/i915/intel_tv.c
index e211eef4b7e4..32186a656816 100644
--- a/drivers/gpu/drm/i915/intel_tv.c
+++ b/drivers/gpu/drm/i915/intel_tv.c
@@ -1323,11 +1323,16 @@ intel_tv_detect(struct drm_connector *connector, bool force)
                 struct intel_load_detect_pipe tmp;
                 struct drm_modeset_acquire_ctx ctx;
 
+                drm_modeset_acquire_init(&ctx, 0);
+
                 if (intel_get_load_detect_pipe(connector, &mode, &tmp, &ctx)) {
                         type = intel_tv_detect_type(intel_tv, connector);
-                        intel_release_load_detect_pipe(connector, &tmp, &ctx);
+                        intel_release_load_detect_pipe(connector, &tmp);
                 } else
                         return connector_status_unknown;
+
+                drm_modeset_drop_locks(&ctx);
+                drm_modeset_acquire_fini(&ctx);
         } else
                 return connector->status;