drm: Add API for capturing frame CRCs

Adds files and directories to debugfs for controlling and reading frame
CRCs, per CRTC:

dri/0/crtc-0/crc
dri/0/crtc-0/crc/control
dri/0/crtc-0/crc/data

Drivers can implement the set_crc_source callback() in drm_crtc_funcs to
start and stop generating frame CRCs and can add entries to the output
by calling drm_crtc_add_crc_entry.

v2:
- Lots of good fixes suggested by Thierry.
- Added documentation.
- Changed the debugfs layout.
- Moved to allocate the entries circular queue once when frame
generation gets enabled for the first time.
v3:
- Use the control file just to select the source, and start and stop
capture when the data file is opened and closed, respectively.
- Make variable the number of CRC values per entry, per source.
- Allocate entries queue each time we start capturing as now there
isn't a fixed number of CRC values per entry.
- Store the frame counter in the data file as a 8-digit hex number.
- For sources that cannot provide useful frame numbers, place
XXXXXXXX in the frame field.

v4:
- Build only if CONFIG_DEBUG_FS is enabled.
- Use memdup_user_nul.
- Consolidate calculation of the size of an entry in a helper.
- Add 0x prefix to hex numbers in the data file.
- Remove unnecessary snprintf and strlen usage in read callback.

v5:
- Made the crcs array in drm_crtc_crc_entry fixed-size
- Lots of other smaller improvements suggested by Emil Velikov

v7:
- Move definition of drm_debugfs_crtc_crc_add to drm_internal.h

v8:
- Call debugfs_remove_recursive when we fail to create the minor
device

v9:
- Register the debugfs directory for a crtc from
drm_crtc_register_all()

v10:
- Don't let debugfs failures interrupt CRTC registration (Emil
Velikov)

v11:
- Remove extra brace that broke compilation. Sorry!

Signed-off-by: Tomeu Vizoso <[e-mail]>
Reviewed-by: Emil Velikov <[e-mail]>
Acked-by: Benjamin Gaignard <[e-mail]>
Signed-off-by: Daniel Vetter <[e-mail]>
Link: http://patchwork.freedesktop.org/patch/msgid/[e-mail]

Documentation/gpu/drm-uapi.rst

···
 userspace are driver specific for efficiency and other reasons these
 interfaces can be rather substantial. Hence every driver has its own
 chapter.
+
+Testing and validation
+======================
+
+.. kernel-doc:: drivers/gpu/drm/drm_debugfs_crc.c
+   :doc: CRC ABI

drivers/gpu/drm/Makefile

···
 		drm_scatter.o drm_pci.o \
 		drm_platform.o drm_sysfs.o drm_hashtab.o drm_mm.o \
 		drm_crtc.o drm_fourcc.o drm_modes.o drm_edid.o \
-		drm_info.o drm_debugfs.o drm_encoder_slave.o \
+		drm_info.o drm_encoder_slave.o \
 		drm_trace_points.o drm_global.o drm_prime.o \
 		drm_rect.o drm_vma_manager.o drm_flip_work.o \
 		drm_modeset_lock.o drm_atomic.o drm_bridge.o \
···
 drm-$(CONFIG_DRM_PANEL) += drm_panel.o
 drm-$(CONFIG_OF) += drm_of.o
 drm-$(CONFIG_AGP) += drm_agpsupport.o
+drm-$(CONFIG_DEBUG_FS) += drm_debugfs.o drm_debugfs_crc.o
 
 drm_kms_helper-y := drm_crtc_helper.o drm_dp_helper.o drm_probe_helper.o \
 		drm_plane_helper.o drm_dp_mst_topology.o drm_atomic_helper.o \

drivers/gpu/drm/drm_crtc.c

···
 #include <drm/drm_modeset_lock.h>
 #include <drm/drm_atomic.h>
 #include <drm/drm_auth.h>
-#include <drm/drm_framebuffer.h>
+#include <drm/drm_debugfs_crc.h>
 
 #include "drm_crtc_internal.h"
 #include "drm_internal.h"
···
 	int ret = 0;
 
 	drm_for_each_crtc(crtc, dev) {
+		if (drm_debugfs_crtc_add(crtc))
+			DRM_ERROR("Failed to initialize debugfs entry for CRTC '%s'.\n",
+				  crtc->name);
+
 		if (crtc->funcs->late_register)
 			ret = crtc->funcs->late_register(crtc);
 		if (ret)
···
 	drm_for_each_crtc(crtc, dev) {
 		if (crtc->funcs->early_unregister)
 			crtc->funcs->early_unregister(crtc);
+		drm_debugfs_crtc_remove(crtc);
 	}
+}
+
+static int drm_crtc_crc_init(struct drm_crtc *crtc)
+{
+#ifdef CONFIG_DEBUG_FS
+	spin_lock_init(&crtc->crc.lock);
+	init_waitqueue_head(&crtc->crc.wq);
+	crtc->crc.source = kstrdup("auto", GFP_KERNEL);
+	if (!crtc->crc.source)
+		return -ENOMEM;
+#endif
+	return 0;
+}
+
+static void drm_crtc_crc_fini(struct drm_crtc *crtc)
+{
+#ifdef CONFIG_DEBUG_FS
+	kfree(crtc->crc.source);
+#endif
 }
 
 /**
···
 	if (cursor)
 		cursor->possible_crtcs = 1 << drm_crtc_index(crtc);
 
+	ret = drm_crtc_crc_init(crtc);
+	if (ret) {
+		drm_mode_object_unregister(dev, &crtc->base);
+		return ret;
+	}
+
 	if (drm_core_check_feature(dev, DRIVER_ATOMIC)) {
 		drm_object_attach_property(&crtc->base, config->prop_active, 0);
 		drm_object_attach_property(&crtc->base, config->prop_mode_id, 0);
···
 	 * remove the drm_crtc at runtime we would have to decrement all
 	 * the indices on the drm_crtc after us in the crtc_list.
 	 */
+
+	drm_crtc_crc_fini(crtc);
 
 	kfree(crtc->gamma_store);
 	crtc->gamma_store = NULL;

drivers/gpu/drm/drm_debugfs.c

···
 	connector->debugfs_entry = NULL;
 }
 
-#endif /* CONFIG_DEBUG_FS */
+int drm_debugfs_crtc_add(struct drm_crtc *crtc)
+{
+	struct drm_minor *minor = crtc->dev->primary;
+	struct dentry *root;
+	char *name;
 
+	name = kasprintf(GFP_KERNEL, "crtc-%d", crtc->index);
+	if (!name)
+		return -ENOMEM;
+
+	root = debugfs_create_dir(name, minor->debugfs_root);
+	kfree(name);
+	if (!root)
+		return -ENOMEM;
+
+	crtc->debugfs_entry = root;
+
+	if (drm_debugfs_crtc_crc_add(crtc))
+		goto error;
+
+	return 0;
+
+error:
+	drm_debugfs_crtc_remove(crtc);
+	return -ENOMEM;
+}
+
+void drm_debugfs_crtc_remove(struct drm_crtc *crtc)
+{
+	debugfs_remove_recursive(crtc->debugfs_entry);
+	crtc->debugfs_entry = NULL;
+}
+
+#endif /* CONFIG_DEBUG_FS */

drivers/gpu/drm/drm_debugfs_crc.c

···
+/*
+ * Copyright © 2008 Intel Corporation
+ * Copyright © 2016 Collabora Ltd
+ *
+ * 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.
+ *
+ * Based on code from the i915 driver.
+ * Original author: Damien Lespiau <[e-mail]>
+ *
+ */
+
+#include <linux/circ_buf.h>
+#include <linux/ctype.h>
+#include <linux/debugfs.h>
+#include <drm/drmP.h>
+
+/**
+ * DOC: CRC ABI
+ *
+ * DRM device drivers can provide to userspace CRC information of each frame as
+ * it reached a given hardware component (a "source").
+ *
+ * Userspace can control generation of CRCs in a given CRTC by writing to the
+ * file dri/0/crtc-N/crc/control in debugfs, with N being the index of the CRTC.
+ * Accepted values are source names (which are driver-specific) and the "auto"
+ * keyword, which will let the driver select a default source of frame CRCs
+ * for this CRTC.
+ *
+ * Once frame CRC generation is enabled, userspace can capture them by reading
+ * the dri/0/crtc-N/crc/data file. Each line in that file contains the frame
+ * number in the first field and then a number of unsigned integer fields
+ * containing the CRC data. Fields are separated by a single space and the number
+ * of CRC fields is source-specific.
+ *
+ * Note that though in some cases the CRC is computed in a specified way and on
+ * the frame contents as supplied by userspace (eDP 1.3), in general the CRC
+ * computation is performed in an unspecified way and on frame contents that have
+ * been already processed in also an unspecified way and thus userspace cannot
+ * rely on being able to generate matching CRC values for the frame contents that
+ * it submits. In this general case, the maximum userspace can do is to compare
+ * the reported CRCs of frames that should have the same contents.
+ */
+
+static int crc_control_show(struct seq_file *m, void *data)
+{
+	struct drm_crtc *crtc = m->private;
+
+	seq_printf(m, "%s\n", crtc->crc.source);
+
+	return 0;
+}
+
+static int crc_control_open(struct inode *inode, struct file *file)
+{
+	struct drm_crtc *crtc = inode->i_private;
+
+	return single_open(file, crc_control_show, crtc);
+}
+
+static ssize_t crc_control_write(struct file *file, const char __user *ubuf,
+				 size_t len, loff_t *offp)
+{
+	struct seq_file *m = file->private_data;
+	struct drm_crtc *crtc = m->private;
+	struct drm_crtc_crc *crc = &crtc->crc;
+	char *source;
+
+	if (len == 0)
+		return 0;
+
+	if (len > PAGE_SIZE - 1) {
+		DRM_DEBUG_KMS("Expected < %lu bytes into crtc crc control\n",
+			      PAGE_SIZE);
+		return -E2BIG;
+	}
+
+	source = memdup_user_nul(ubuf, len);
+	if (IS_ERR(source))
+		return PTR_ERR(source);
+
+	if (source[len] == '\n')
+		source[len] = '\0';
+
+	spin_lock_irq(&crc->lock);
+
+	if (crc->opened) {
+		spin_unlock_irq(&crc->lock);
+		kfree(source);
+		return -EBUSY;
+	}
+
+	kfree(crc->source);
+	crc->source = source;
+
+	spin_unlock_irq(&crc->lock);
+
+	*offp += len;
+	return len;
+}
+
+const struct file_operations drm_crtc_crc_control_fops = {
+	.owner = THIS_MODULE,
+	.open = crc_control_open,
+	.read = seq_read,
+	.llseek = seq_lseek,
+	.release = single_release,
+	.write = crc_control_write
+};
+
+static int crtc_crc_open(struct inode *inode, struct file *filep)
+{
+	struct drm_crtc *crtc = inode->i_private;
+	struct drm_crtc_crc *crc = &crtc->crc;
+	struct drm_crtc_crc_entry *entries = NULL;
+	size_t values_cnt;
+	int ret;
+
+	if (crc->opened)
+		return -EBUSY;
+
+	ret = crtc->funcs->set_crc_source(crtc, crc->source, &values_cnt);
+	if (ret)
+		return ret;
+
+	if (WARN_ON(values_cnt > DRM_MAX_CRC_NR)) {
+		ret = -EINVAL;
+		goto err_disable;
+	}
+
+	if (WARN_ON(values_cnt == 0)) {
+		ret = -EINVAL;
+		goto err_disable;
+	}
+
+	entries = kcalloc(DRM_CRC_ENTRIES_NR, sizeof(*entries), GFP_KERNEL);
+	if (!entries) {
+		ret = -ENOMEM;
+		goto err_disable;
+	}
+
+	spin_lock_irq(&crc->lock);
+	crc->entries = entries;
+	crc->values_cnt = values_cnt;
+	crc->opened = true;
+	spin_unlock_irq(&crc->lock);
+
+	return 0;
+
+err_disable:
+	crtc->funcs->set_crc_source(crtc, NULL, &values_cnt);
+	return ret;
+}
+
+static int crtc_crc_release(struct inode *inode, struct file *filep)
+{
+	struct drm_crtc *crtc = filep->f_inode->i_private;
+	struct drm_crtc_crc *crc = &crtc->crc;
+	size_t values_cnt;
+
+	spin_lock_irq(&crc->lock);
+	kfree(crc->entries);
+	crc->entries = NULL;
+	crc->head = 0;
+	crc->tail = 0;
+	crc->values_cnt = 0;
+	crc->opened = false;
+	spin_unlock_irq(&crc->lock);
+
+	crtc->funcs->set_crc_source(crtc, NULL, &values_cnt);
+
+	return 0;
+}
+
+static int crtc_crc_data_count(struct drm_crtc_crc *crc)
+{
+	assert_spin_locked(&crc->lock);
+	return CIRC_CNT(crc->head, crc->tail, DRM_CRC_ENTRIES_NR);
+}
+
+/*
+ * 1 frame field of 10 chars plus a number of CRC fields of 10 chars each, space
+ * separated, with a newline at the end and null-terminated.
+ */
+#define LINE_LEN(values_cnt)	(10 + 11 * values_cnt + 1 + 1)
+#define MAX_LINE_LEN		(LINE_LEN(DRM_MAX_CRC_NR))
+
+static ssize_t crtc_crc_read(struct file *filep, char __user *user_buf,
+			     size_t count, loff_t *pos)
+{
+	struct drm_crtc *crtc = filep->f_inode->i_private;
+	struct drm_crtc_crc *crc = &crtc->crc;
+	struct drm_crtc_crc_entry *entry;
+	char buf[MAX_LINE_LEN];
+	int ret, i;
+
+	spin_lock_irq(&crc->lock);
+
+	if (!crc->source) {
+		spin_unlock_irq(&crc->lock);
+		return 0;
+	}
+
+	/* Nothing to read? */
+	while (crtc_crc_data_count(crc) == 0) {
+		if (filep->f_flags & O_NONBLOCK) {
+			spin_unlock_irq(&crc->lock);
+			return -EAGAIN;
+		}
+
+		ret = wait_event_interruptible_lock_irq(crc->wq,
+							crtc_crc_data_count(crc),
+							crc->lock);
+		if (ret) {
+			spin_unlock_irq(&crc->lock);
+			return ret;
+		}
+	}
+
+	/* We know we have an entry to be read */
+	entry = &crc->entries[crc->tail];
+
+	if (count < LINE_LEN(crc->values_cnt)) {
+		spin_unlock_irq(&crc->lock);
+		return -EINVAL;
+	}
+
+	BUILD_BUG_ON_NOT_POWER_OF_2(DRM_CRC_ENTRIES_NR);
+	crc->tail = (crc->tail + 1) & (DRM_CRC_ENTRIES_NR - 1);
+
+	spin_unlock_irq(&crc->lock);
+
+	if (entry->has_frame_counter)
+		sprintf(buf, "0x%08x", entry->frame);
+	else
+		sprintf(buf, "XXXXXXXXXX");
+
+	for (i = 0; i < crc->values_cnt; i++)
+		sprintf(buf + 10 + i * 11, " 0x%08x", entry->crcs[i]);
+	sprintf(buf + 10 + crc->values_cnt * 11, "\n");
+
+	if (copy_to_user(user_buf, buf, LINE_LEN(crc->values_cnt)))
+		return -EFAULT;
+
+	return LINE_LEN(crc->values_cnt);
+}
+
+const struct file_operations drm_crtc_crc_data_fops = {
+	.owner = THIS_MODULE,
+	.open = crtc_crc_open,
+	.read = crtc_crc_read,
+	.release = crtc_crc_release,
+};
+
+/**
+ * drm_debugfs_crtc_crc_add - Add files to debugfs for capture of frame CRCs
+ * @crtc: CRTC to whom the frames will belong
+ *
+ * Adds files to debugfs directory that allows userspace to control the
+ * generation of frame CRCs and to read them.
+ *
+ * Returns:
+ * Zero on success, error code on failure.
+ */
+int drm_debugfs_crtc_crc_add(struct drm_crtc *crtc)
+{
+	struct dentry *crc_ent, *ent;
+
+	if (!crtc->funcs->set_crc_source)
+		return 0;
+
+	crc_ent = debugfs_create_dir("crc", crtc->debugfs_entry);
+	if (!crc_ent)
+		return -ENOMEM;
+
+	ent = debugfs_create_file("control", S_IRUGO, crc_ent, crtc,
+				  &drm_crtc_crc_control_fops);
+	if (!ent)
+		goto error;
+
+	ent = debugfs_create_file("data", S_IRUGO, crc_ent, crtc,
+				  &drm_crtc_crc_data_fops);
+	if (!ent)
+		goto error;
+
+	return 0;
+
+error:
+	debugfs_remove_recursive(crc_ent);
+
+	return -ENOMEM;
+}
+
+/**
+ * drm_crtc_add_crc_entry - Add entry with CRC information for a frame
+ * @crtc: CRTC to which the frame belongs
+ * @has_frame: whether this entry has a frame number to go with
+ * @frame: number of the frame these CRCs are about
+ * @crcs: array of CRC values, with length matching #drm_crtc_crc.values_cnt
+ *
+ * For each frame, the driver polls the source of CRCs for new data and calls
+ * this function to add them to the buffer from where userspace reads.
+ */
+int drm_crtc_add_crc_entry(struct drm_crtc *crtc, bool has_frame,
+			   uint32_t frame, uint32_t *crcs)
+{
+	struct drm_crtc_crc *crc = &crtc->crc;
+	struct drm_crtc_crc_entry *entry;
+	int head, tail;
+
+	assert_spin_locked(&crc->lock);
+
+	/* Caller may not have noticed yet that userspace has stopped reading */
+	if (!crc->opened)
+		return -EINVAL;
+
+	head = crc->head;
+	tail = crc->tail;
+
+	if (CIRC_SPACE(head, tail, DRM_CRC_ENTRIES_NR) < 1) {
+		DRM_ERROR("Overflow of CRC buffer, userspace reads too slow.\n");
+		return -ENOBUFS;
+	}
+
+	entry = &crc->entries[head];
+	entry->frame = frame;
+	entry->has_frame_counter = has_frame;
+	memcpy(&entry->crcs, crcs, sizeof(*crcs) * crc->values_cnt);
+
+	head = (head + 1) & (DRM_CRC_ENTRIES_NR - 1);
+	crc->head = head;
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(drm_crtc_add_crc_entry);

drivers/gpu/drm/drm_internal.h

···
 int drm_debugfs_cleanup(struct drm_minor *minor);
 int drm_debugfs_connector_add(struct drm_connector *connector);
 void drm_debugfs_connector_remove(struct drm_connector *connector);
+int drm_debugfs_crtc_add(struct drm_crtc *crtc);
+void drm_debugfs_crtc_remove(struct drm_crtc *crtc);
+int drm_debugfs_crtc_crc_add(struct drm_crtc *crtc);
 #else
 static inline int drm_debugfs_init(struct drm_minor *minor, int minor_id,
 				   struct dentry *root)
···
 }
 static inline void drm_debugfs_connector_remove(struct drm_connector *connector)
 {
+}
+
+static inline int drm_debugfs_crtc_add(struct drm_crtc *crtc)
+{
+	return 0;
+}
+static inline void drm_debugfs_crtc_remove(struct drm_crtc *crtc)
+{
+}
+
+static inline int drm_debugfs_crtc_crc_add(struct drm_crtc *crtc)
+{
+	return 0;
 }
 #endif

include/drm/drm_crtc.h

···
 #include <drm/drm_plane.h>
 #include <drm/drm_blend.h>
 #include <drm/drm_color_mgmt.h>
+#include <drm/drm_debugfs_crc.h>
 
 struct drm_device;
 struct drm_mode_set;
···
 	 * before data structures are torndown.
 	 */
 	void (*early_unregister)(struct drm_crtc *crtc);
+
+	/**
+	 * @set_crc_source:
+	 *
+	 * Changes the source of CRC checksums of frames at the request of
+	 * userspace, typically for testing purposes. The sources available are
+	 * specific of each driver and a %NULL value indicates that CRC
+	 * generation is to be switched off.
+	 *
+	 * When CRC generation is enabled, the driver should call
+	 * drm_crtc_add_crc_entry() at each frame, providing any information
+	 * that characterizes the frame contents in the crcN arguments, as
+	 * provided from the configured source. Drivers must accept a "auto"
+	 * source name that will select a default source for this CRTC.
+	 *
+	 * This callback is optional if the driver does not support any CRC
+	 * generation functionality.
+	 *
+	 * RETURNS:
+	 *
+	 * 0 on success or a negative error code on failure.
+	 */
+	int (*set_crc_source)(struct drm_crtc *crtc, const char *source,
+			      size_t *values_cnt);
 };
 
 /**
···
 	 * context.
 	 */
 	struct drm_modeset_acquire_ctx *acquire_ctx;
+
+#ifdef CONFIG_DEBUG_FS
+	/**
+	 * @debugfs_entry:
+	 *
+	 * Debugfs directory for this CRTC.
+	 */
+	struct dentry *debugfs_entry;
+
+	/**
+	 * @crc:
+	 *
+	 * Configuration settings of CRC capture.
+	 */
+	struct drm_crtc_crc crc;
+#endif
 };
 
 /**

include/drm/drm_debugfs_crc.h

···
+/*
+ * Copyright © 2016 Collabora Ltd.
+ *
+ * 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 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 COPYRIGHT HOLDER(S) OR AUTHOR(S) 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_DEBUGFS_CRC_H__
+#define __DRM_DEBUGFS_CRC_H__
+
+#define DRM_MAX_CRC_NR		10
+
+/**
+ * struct drm_crtc_crc_entry - entry describing a frame's content
+ * @has_frame_counter: whether the source was able to provide a frame number
+ * @frame: number of the frame this CRC is about, if @has_frame_counter is true
+ * @crc: array of values that characterize the frame
+ */
+struct drm_crtc_crc_entry {
+	bool has_frame_counter;
+	uint32_t frame;
+	uint32_t crcs[DRM_MAX_CRC_NR];
+};
+
+#define DRM_CRC_ENTRIES_NR	128
+
+/**
+ * struct drm_crtc_crc - data supporting CRC capture on a given CRTC
+ * @lock: protects the fields in this struct
+ * @source: name of the currently configured source of CRCs
+ * @opened: whether userspace has opened the data file for reading
+ * @entries: array of entries, with size of %DRM_CRC_ENTRIES_NR
+ * @head: head of circular queue
+ * @tail: tail of circular queue
+ * @values_cnt: number of CRC values per entry, up to %DRM_MAX_CRC_NR
+ * @wq: workqueue used to synchronize reading and writing
+ */
+struct drm_crtc_crc {
+	spinlock_t lock;
+	const char *source;
+	bool opened;
+	struct drm_crtc_crc_entry *entries;
+	int head, tail;
+	size_t values_cnt;
+	wait_queue_head_t wq;
+};
+
+#if defined(CONFIG_DEBUG_FS)
+int drm_crtc_add_crc_entry(struct drm_crtc *crtc, bool has_frame,
+			   uint32_t frame, uint32_t *crcs);
+#else
+static inline int drm_crtc_add_crc_entry(struct drm_crtc *crtc, bool has_frame,
+					 uint32_t frame, uint32_t *crcs)
+{
+	return -EINVAL;
+}
+#endif /* defined(CONFIG_DEBUG_FS) */
+
+#endif /* __DRM_DEBUGFS_CRC_H__ */