linux-kernel - [PATCH v2 3/3] drm: Expose CRTC's kworker task id

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Message-Id: <20200930211723.3028059-4-robdclark@gmail.com>
Date:   Wed, 30 Sep 2020 14:17:22 -0700
From:   Rob Clark <robdclark@...il.com>
To:     dri-devel@...ts.freedesktop.org
Cc:     linux-arm-msm@...r.kernel.org, Tejun Heo <tj@...nel.org>,
        timmurray@...gle.com, Daniel Vetter <daniel@...ll.ch>,
        Qais Yousef <qais.yousef@....com>,
        Rob Clark <robdclark@...omium.org>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        David Airlie <airlied@...ux.ie>,
        linux-kernel@...r.kernel.org (open list)
Subject: [PATCH v2 3/3] drm: Expose CRTC's kworker task id

From: Rob Clark <robdclark@...omium.org>

This will allow userspace to control the scheduling policy and priority.
In particular if the userspace half of the display pipeline is SCHED_FIFO
then it will want to use the same scheduling policy and an appropriate
priority to ensure that it is not preempting commit_work.

Signed-off-by: Rob Clark <robdclark@...omium.org>
---
 drivers/gpu/drm/drm_crtc.c        |  3 +++
 drivers/gpu/drm/drm_mode_config.c | 14 ++++++++++++++
 drivers/gpu/drm/drm_mode_object.c |  4 ++++
 include/drm/drm_mode_config.h     |  9 +++++++++
 include/drm/drm_property.h        |  9 +++++++++
 5 files changed, 39 insertions(+)

diff --git a/drivers/gpu/drm/drm_crtc.c b/drivers/gpu/drm/drm_crtc.c
index 4f7c0bfce0a3..1828853542dc 100644
--- a/drivers/gpu/drm/drm_crtc.c
+++ b/drivers/gpu/drm/drm_crtc.c
@@ -334,6 +334,9 @@ int drm_crtc_init_with_planes(struct drm_device *dev, struct drm_crtc *crtc,
 			crtc->worker = NULL;
 			return ret;
 		}
+
+		drm_object_attach_property(&crtc->base,
+					   config->kwork_tid_property, 0);
 	}
 
 	return 0;
diff --git a/drivers/gpu/drm/drm_mode_config.c b/drivers/gpu/drm/drm_mode_config.c
index f1affc1bb679..b11a1fc8ed0d 100644
--- a/drivers/gpu/drm/drm_mode_config.c
+++ b/drivers/gpu/drm/drm_mode_config.c
@@ -215,6 +215,13 @@ static const struct drm_prop_enum_list drm_plane_type_enum_list[] = {
 	{ DRM_PLANE_TYPE_CURSOR, "Cursor" },
 };
 
+static int get_kwork_tid(struct drm_mode_object *obj, uint64_t *val)
+{
+	struct drm_crtc *crtc = obj_to_crtc(obj);
+	*val = task_pid_vnr(crtc->worker->task);
+	return 0;
+}
+
 static int drm_mode_create_standard_properties(struct drm_device *dev)
 {
 	struct drm_property *prop;
@@ -371,6 +378,13 @@ static int drm_mode_create_standard_properties(struct drm_device *dev)
 		return -ENOMEM;
 	dev->mode_config.modifiers_property = prop;
 
+	prop = drm_property_create_range(dev, DRM_MODE_PROP_ATOMIC,
+			"KWORK_TID", 0, UINT_MAX);
+	if (!prop)
+		return -ENOMEM;
+	prop->get_value = get_kwork_tid;
+	dev->mode_config.kwork_tid_property = prop;
+
 	return 0;
 }
 
diff --git a/drivers/gpu/drm/drm_mode_object.c b/drivers/gpu/drm/drm_mode_object.c
index db05f386a709..1a4df65baf0f 100644
--- a/drivers/gpu/drm/drm_mode_object.c
+++ b/drivers/gpu/drm/drm_mode_object.c
@@ -285,6 +285,7 @@ int drm_object_property_set_value(struct drm_mode_object *obj,
 
 	WARN_ON(drm_drv_uses_atomic_modeset(property->dev) &&
 		!(property->flags & DRM_MODE_PROP_IMMUTABLE));
+	WARN_ON(property->get_value);
 
 	for (i = 0; i < obj->properties->count; i++) {
 		if (obj->properties->properties[i] == property) {
@@ -303,6 +304,9 @@ static int __drm_object_property_get_value(struct drm_mode_object *obj,
 {
 	int i;
 
+	if (property->get_value)
+		return property->get_value(obj, val);
+
 	/* read-only properties bypass atomic mechanism and still store
 	 * their value in obj->properties->values[].. mostly to avoid
 	 * having to deal w/ EDID and similar props in atomic paths:
diff --git a/include/drm/drm_mode_config.h b/include/drm/drm_mode_config.h
index c2d3d71d133c..7244df926a6d 100644
--- a/include/drm/drm_mode_config.h
+++ b/include/drm/drm_mode_config.h
@@ -926,6 +926,15 @@ struct drm_mode_config {
 	 */
 	struct drm_property *modifiers_property;
 
+	/**
+	 * @kwork_tid_property: CRTC property to expose the task-id of the per-
+	 * CRTC kthread-worker, used for non-block atomic commit.  This is exposed
+	 * to userspace, to allow userspace to control the scheduling policy and
+	 * priority, as this is a decision that depends on how userspace structures
+	 * it's rendering pipeline.
+	 */
+	struct drm_property *kwork_tid_property;
+
 	/* cursor size */
 	uint32_t cursor_width, cursor_height;
 
diff --git a/include/drm/drm_property.h b/include/drm/drm_property.h
index 4a0a80d658c7..6843be6aa3ec 100644
--- a/include/drm/drm_property.h
+++ b/include/drm/drm_property.h
@@ -188,6 +188,15 @@ struct drm_property {
 	 * enum and bitmask values.
 	 */
 	struct list_head enum_list;
+
+	/**
+	 * @get_value: accessor to get current value for "virtual" properties
+	 *
+	 * For properties with dynamic values, where it is for whatever reason
+	 * not feasible to keep updated with drm_object_property_set_value(),
+	 * this callback can be used to retrieve the current value on demand.
+	 */
+	int (*get_value)(struct drm_mode_object *obj, uint64_t *val);
 };
 
 /**
-- 
2.26.2