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authorLukas Wunner <lukas@wunner.de>2018-02-14 06:41:25 +0100
committerLukas Wunner <lukas@wunner.de>2018-02-16 22:30:06 +0100
commit25c058ccaf2ebbc3e250ec1e199e161f91fe27d4 (patch)
tree93aa786dec9bd0d10648ea885444f78b36daceb9
parent27d4ee03078aba88c5e07dcc4917e8d01d046f38 (diff)
drm: Allow determining if current task is output poll worker
Introduce a helper to determine if the current task is an output poll worker. This allows us to fix a long-standing deadlock in several DRM drivers wherein the ->runtime_suspend callback waits for the output poll worker to finish and the worker in turn calls a ->detect callback which waits for runtime suspend to finish. The ->detect callback is invoked from multiple call sites and waiting for runtime suspend to finish is the correct thing to do except if it's executing in the context of the worker. v2: Expand kerneldoc to specifically mention deadlock between output poll worker and autosuspend worker as use case. (Lyude) Cc: Dave Airlie <airlied@redhat.com> Cc: Ben Skeggs <bskeggs@redhat.com> Cc: Alex Deucher <alexander.deucher@amd.com> Reviewed-by: Lyude Paul <lyude@redhat.com> Signed-off-by: Lukas Wunner <lukas@wunner.de> Link: https://patchwork.freedesktop.org/patch/msgid/3549ce32e7f1467102e70d3e9cbf70c46bfe108e.1518593424.git.lukas@wunner.de
-rw-r--r--drivers/gpu/drm/drm_probe_helper.c20
-rw-r--r--include/drm/drm_crtc_helper.h1
2 files changed, 21 insertions, 0 deletions
diff --git a/drivers/gpu/drm/drm_probe_helper.c b/drivers/gpu/drm/drm_probe_helper.c
index 6dc2dde5b672..7a6b2dc08913 100644
--- a/drivers/gpu/drm/drm_probe_helper.c
+++ b/drivers/gpu/drm/drm_probe_helper.c
@@ -655,6 +655,26 @@ out:
}
/**
+ * drm_kms_helper_is_poll_worker - is %current task an output poll worker?
+ *
+ * Determine if %current task is an output poll worker. This can be used
+ * to select distinct code paths for output polling versus other contexts.
+ *
+ * One use case is to avoid a deadlock between the output poll worker and
+ * the autosuspend worker wherein the latter waits for polling to finish
+ * upon calling drm_kms_helper_poll_disable(), while the former waits for
+ * runtime suspend to finish upon calling pm_runtime_get_sync() in a
+ * connector ->detect hook.
+ */
+bool drm_kms_helper_is_poll_worker(void)
+{
+ struct work_struct *work = current_work();
+
+ return work && work->func == output_poll_execute;
+}
+EXPORT_SYMBOL(drm_kms_helper_is_poll_worker);
+
+/**
* drm_kms_helper_poll_disable - disable output polling
* @dev: drm_device
*
diff --git a/include/drm/drm_crtc_helper.h b/include/drm/drm_crtc_helper.h
index 76e237bd989b..6914633037a5 100644
--- a/include/drm/drm_crtc_helper.h
+++ b/include/drm/drm_crtc_helper.h
@@ -77,5 +77,6 @@ void drm_kms_helper_hotplug_event(struct drm_device *dev);
void drm_kms_helper_poll_disable(struct drm_device *dev);
void drm_kms_helper_poll_enable(struct drm_device *dev);
+bool drm_kms_helper_is_poll_worker(void);
#endif