drm: add flip-work helper

A small helper to queue up work to do, from workqueue context, after a
flip. Typically useful to defer unreffing buffers that may be read by
the display controller until vblank.

v1: original
v2: wire up docbook + couple docbook fixes

Signed-off-by: Rob Clark <[e-mail]>
Acked-by: Daniel Vetter <[e-mail]>
Signed-off-by: Dave Airlie <[e-mail]>

Documentation/DocBook/drm.tmpl

···
 !Edrivers/gpu/drm/drm_rect.c
     </sect2>
     <sect2>
+      <title>Flip-work Helper Reference</title>
+!Pinclude/drm/drm_flip_work.h flip utils
+!Iinclude/drm/drm_flip_work.h
+!Edrivers/gpu/drm/drm_flip_work.c
+    </sect2>
+    <sect2>
       <title>VMA Offset Manager</title>
 !Pdrivers/gpu/drm/drm_vma_manager.c vma offset manager
 !Edrivers/gpu/drm/drm_vma_manager.c

drivers/gpu/drm/Makefile

···
 		drm_crtc.o drm_modes.o drm_edid.o \
 		drm_info.o drm_debugfs.o drm_encoder_slave.o \
 		drm_trace_points.o drm_global.o drm_prime.o \
-		drm_rect.o drm_vma_manager.o
+		drm_rect.o drm_vma_manager.o drm_flip_work.o
 
 drm-$(CONFIG_COMPAT) += drm_ioc32.o
 drm-$(CONFIG_DRM_GEM_CMA_HELPER) += drm_gem_cma_helper.o

drivers/gpu/drm/drm_flip_work.c

···
+/*
+ * Copyright (C) 2013 Red Hat
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a
+ * copy of this software and associated documentation files (the "Software"),
+ * to deal in the Software without restriction, including without limitation
+ * the rights to use, copy, modify, merge, publish, distribute, sublicense,
+ * and/or sell copies of the Software, and to permit persons to whom the
+ * Software is furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice (including the next
+ * paragraph) shall be included in all copies or substantial portions of the
+ * Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
+ * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ */
+
+#include "drmP.h"
+#include "drm_flip_work.h"
+
+/**
+ * drm_flip_work_queue - queue work
+ * @work: the flip-work
+ * @val: the value to queue
+ *
+ * Queues work, that will later be run (passed back to drm_flip_func_t
+ * func) on a work queue after drm_flip_work_commit() is called.
+ */
+void drm_flip_work_queue(struct drm_flip_work *work, void *val)
+{
+	if (kfifo_put(&work->fifo, (const void **)&val)) {
+		atomic_inc(&work->pending);
+	} else {
+		DRM_ERROR("%s fifo full!\n", work->name);
+		work->func(work, val);
+	}
+}
+EXPORT_SYMBOL(drm_flip_work_queue);
+
+/**
+ * drm_flip_work_commit - commit queued work
+ * @work: the flip-work
+ * @wq: the work-queue to run the queued work on
+ *
+ * Trigger work previously queued by drm_flip_work_queue() to run
+ * on a workqueue.  The typical usage would be to queue work (via
+ * drm_flip_work_queue()) at any point (from vblank irq and/or
+ * prior), and then from vblank irq commit the queued work.
+ */
+void drm_flip_work_commit(struct drm_flip_work *work,
+		struct workqueue_struct *wq)
+{
+	uint32_t pending = atomic_read(&work->pending);
+	atomic_add(pending, &work->count);
+	atomic_sub(pending, &work->pending);
+	queue_work(wq, &work->worker);
+}
+EXPORT_SYMBOL(drm_flip_work_commit);
+
+static void flip_worker(struct work_struct *w)
+{
+	struct drm_flip_work *work = container_of(w, struct drm_flip_work, worker);
+	uint32_t count = atomic_read(&work->count);
+	void *val = NULL;
+
+	atomic_sub(count, &work->count);
+
+	while(count--)
+		if (!WARN_ON(!kfifo_get(&work->fifo, &val)))
+			work->func(work, val);
+}
+
+/**
+ * drm_flip_work_init - initialize flip-work
+ * @work: the flip-work to initialize
+ * @size: the max queue depth
+ * @name: debug name
+ * @func: the callback work function
+ *
+ * Initializes/allocates resources for the flip-work
+ *
+ * RETURNS:
+ * Zero on success, error code on failure.
+ */
+int drm_flip_work_init(struct drm_flip_work *work, int size,
+		const char *name, drm_flip_func_t func)
+{
+	int ret;
+
+	work->name = name;
+	atomic_set(&work->count, 0);
+	atomic_set(&work->pending, 0);
+	work->func = func;
+
+	ret = kfifo_alloc(&work->fifo, size, GFP_KERNEL);
+	if (ret) {
+		DRM_ERROR("could not allocate %s fifo\n", name);
+		return ret;
+	}
+
+	INIT_WORK(&work->worker, flip_worker);
+
+	return 0;
+}
+EXPORT_SYMBOL(drm_flip_work_init);
+
+/**
+ * drm_flip_work_cleanup - cleans up flip-work
+ * @work: the flip-work to cleanup
+ *
+ * Destroy resources allocated for the flip-work
+ */
+void drm_flip_work_cleanup(struct drm_flip_work *work)
+{
+	WARN_ON(!kfifo_is_empty(&work->fifo));
+	kfifo_free(&work->fifo);
+}
+EXPORT_SYMBOL(drm_flip_work_cleanup);

include/drm/drm_flip_work.h

···
+/*
+ * Copyright (C) 2013 Red Hat
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a
+ * copy of this software and associated documentation files (the "Software"),
+ * to deal in the Software without restriction, including without limitation
+ * the rights to use, copy, modify, merge, publish, distribute, sublicense,
+ * and/or sell copies of the Software, and to permit persons to whom the
+ * Software is furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice (including the next
+ * paragraph) shall be included in all copies or substantial portions of the
+ * Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
+ * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ */
+
+#ifndef DRM_FLIP_WORK_H
+#define DRM_FLIP_WORK_H
+
+#include <linux/kfifo.h>
+#include <linux/workqueue.h>
+
+/**
+ * DOC: flip utils
+ *
+ * Util to queue up work to run from work-queue context after flip/vblank.
+ * Typically this can be used to defer unref of framebuffer's, cursor
+ * bo's, etc until after vblank.  The APIs are all safe (and lockless)
+ * for up to one producer and once consumer at a time.  The single-consumer
+ * aspect is ensured by committing the queued work to a single work-queue.
+ */
+
+struct drm_flip_work;
+
+/*
+ * drm_flip_func_t - callback function
+ *
+ * @work: the flip work
+ * @val: value queued via drm_flip_work_queue()
+ *
+ * Callback function to be called for each of the  queue'd work items after
+ * drm_flip_work_commit() is called.
+ */
+typedef void (*drm_flip_func_t)(struct drm_flip_work *work, void *val);
+
+/**
+ * struct drm_flip_work - flip work queue
+ * @name: debug name
+ * @pending: number of queued but not committed items
+ * @count: number of committed items
+ * @func: callback fxn called for each committed item
+ * @worker: worker which calls @func
+ */
+struct drm_flip_work {
+	const char *name;
+	atomic_t pending, count;
+	drm_flip_func_t func;
+	struct work_struct worker;
+	DECLARE_KFIFO_PTR(fifo, void *);
+};
+
+void drm_flip_work_queue(struct drm_flip_work *work, void *val);
+void drm_flip_work_commit(struct drm_flip_work *work,
+		struct workqueue_struct *wq);
+int drm_flip_work_init(struct drm_flip_work *work, int size,
+		const char *name, drm_flip_func_t func);
+void drm_flip_work_cleanup(struct drm_flip_work *work);
+
+#endif  /* DRM_FLIP_WORK_H */