[PATCH] drm/vc4: Add a debugfs entry to disable/enable the load tracker

[Paul Kocialkowski]

In order to test whether the load tracker is working as expected, we
need the ability to compare the commit result with the underrun
indication. With the load tracker always enabled, commits that are
expected to trigger an underrun are always rejected, so userspace
cannot get the actual underrun indication from the hardware.

Add a debugfs entry to disable/enable the load tracker, so that a DRM
commit expected to trigger an underrun can go through with the load
tracker disabled. The underrun indication is then available to
userspace and can be checked against the commit result with the load
tracker enabled.

Signed-off-by: Paul Kocialkowski <paul.kocialkowski at bootlin.com>
---

This patch is based on Boris Brezillion's series: drm/vc4: Add a load tracker.

 drivers/gpu/drm/vc4/vc4_debugfs.c |  8 +++++
 drivers/gpu/drm/vc4/vc4_drv.c     | 52 +++++++++++++++++++++++++++++++
 drivers/gpu/drm/vc4/vc4_drv.h     |  3 ++
 drivers/gpu/drm/vc4/vc4_kms.c     |  6 +++-
 4 files changed, 68 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/vc4/vc4_debugfs.c b/drivers/gpu/drm/vc4/vc4_debugfs.c
index 7a0003de71ab..250fee440aac 100644
--- a/drivers/gpu/drm/vc4/vc4_debugfs.c
+++ b/drivers/gpu/drm/vc4/vc4_debugfs.c
@@ -35,6 +35,14 @@ static const struct drm_info_list vc4_debugfs_list[] = {
 int
 vc4_debugfs_init(struct drm_minor *minor)
 {
+	struct dentry *dentry;
+
+	dentry = debugfs_create_file("load_tracker", S_IRUGO | S_IWUSR,
+				     minor->debugfs_root, minor->dev,
+				     &vc4_debugfs_load_tracker_fops);
+	if (!dentry)
+		return -ENOMEM;
+
 	return drm_debugfs_create_files(vc4_debugfs_list, VC4_DEBUGFS_ENTRIES,
 					minor->debugfs_root, minor);
 }
diff --git a/drivers/gpu/drm/vc4/vc4_drv.c b/drivers/gpu/drm/vc4/vc4_drv.c
index 7195a0bcceb3..0ee75c71d8d8 100644
--- a/drivers/gpu/drm/vc4/vc4_drv.c
+++ b/drivers/gpu/drm/vc4/vc4_drv.c
@@ -46,6 +46,56 @@
 #define DRIVER_MINOR 0
 #define DRIVER_PATCHLEVEL 0
 
+static int vc4_debugfs_load_tracker_get(struct seq_file *m, void *data)
+{
+	struct drm_device *dev = m->private;
+	struct vc4_dev *vc4 = to_vc4_dev(dev);
+
+	if (vc4->load_tracker_enabled)
+		seq_printf(m, "enabled\n");
+	else
+		seq_printf(m, "disabled\n");
+
+	return 0;
+}
+
+static ssize_t vc4_debugfs_load_tracker_set(struct file *file,
+					    const char __user *ubuf,
+					    size_t len, loff_t *offp)
+{
+	struct seq_file *m = file->private_data;
+	struct drm_device *dev = m->private;
+	struct vc4_dev *vc4 = to_vc4_dev(dev);
+	char buf[32] = {};
+
+	if (len >= sizeof(buf))
+		return -EINVAL;
+
+	if (copy_from_user(buf, ubuf, len))
+		return -EFAULT;
+
+	if (!strncasecmp(buf, "enable", 6))
+		vc4->load_tracker_enabled = true;
+	else if (!strncasecmp(buf, "disable", 7))
+		vc4->load_tracker_enabled = false;
+	else
+		return -EINVAL;
+
+	return len;
+}
+
+static int vc4_debugfs_load_tracker_open(struct inode *inode, struct file *file)
+{
+	return single_open(file, vc4_debugfs_load_tracker_get, inode->i_private);
+}
+
+const struct file_operations vc4_debugfs_load_tracker_fops = {
+	.owner = THIS_MODULE,
+	.open = vc4_debugfs_load_tracker_open,
+	.read = seq_read,
+	.write = vc4_debugfs_load_tracker_set,
+};
+
 /* Helper function for mapping the regs on a platform device. */
 void __iomem *vc4_ioremap_regs(struct platform_device *dev, int index)
 {
@@ -290,6 +340,8 @@ static int vc4_drm_bind(struct device *dev)
 
 	drm_fbdev_generic_setup(drm, 32);
 
+	vc4->load_tracker_enabled = true;
+
 	return 0;
 
 unbind_all:
diff --git a/drivers/gpu/drm/vc4/vc4_drv.h b/drivers/gpu/drm/vc4/vc4_drv.h
index 11369da944b6..1344c4d996c4 100644
--- a/drivers/gpu/drm/vc4/vc4_drv.h
+++ b/drivers/gpu/drm/vc4/vc4_drv.h
@@ -188,6 +188,8 @@ struct vc4_dev {
 
 	int power_refcount;
 
+	bool load_tracker_enabled;
+
 	/* Mutex controlling the power refcount. */
 	struct mutex power_lock;
 
@@ -717,6 +719,7 @@ void vc4_crtc_txp_armed(struct drm_crtc_state *state);
 int vc4_debugfs_init(struct drm_minor *minor);
 
 /* vc4_drv.c */
+extern const struct file_operations vc4_debugfs_load_tracker_fops;
 void __iomem *vc4_ioremap_regs(struct platform_device *dev, int index);
 
 /* vc4_dpi.c */
diff --git a/drivers/gpu/drm/vc4/vc4_kms.c b/drivers/gpu/drm/vc4/vc4_kms.c
index b905a19c1470..4b2509b1b8ed 100644
--- a/drivers/gpu/drm/vc4/vc4_kms.c
+++ b/drivers/gpu/drm/vc4/vc4_kms.c
@@ -473,6 +473,7 @@ static const struct drm_private_state_funcs vc4_load_tracker_state_funcs = {
 static int
 vc4_atomic_check(struct drm_device *dev, struct drm_atomic_state *state)
 {
+	struct vc4_dev *vc4 = to_vc4_dev(dev);
 	int ret;
 
 	ret = vc4_ctm_atomic_check(dev, state);
@@ -483,7 +484,10 @@ vc4_atomic_check(struct drm_device *dev, struct drm_atomic_state *state)
 	if (ret)
 		return ret;
 
-	return vc4_load_tracker_atomic_check(state);
+	if (vc4->load_tracker_enabled)
+		return vc4_load_tracker_atomic_check(state);
+
+	return 0;
 }
 
 static const struct drm_mode_config_funcs vc4_mode_funcs = {
-- 
2.19.1