Re: [PATCH v2] drm/vc4: Add a debugfs entry to disable/enable the load tracker

[Paul Kocialkowski <paul.kocialkowski@bootlin.com>]

Hi Boris,

Le vendredi 30 novembre 2018 à 19:57 +0100, Boris Brezillon a écrit :
> On Fri, 30 Nov 2018 17:11:04 +0100
> Paul Kocialkowski <paul.kocialkowski@bootlin.com> wrote:
> 
> > 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@bootlin.com>
> > ---
> > 
> > Changes since v1:
> > * Moved all the debugfs-related functions and structure to vc4_debugfs.c.
> > 
> >  drivers/gpu/drm/vc4/vc4_debugfs.c | 58 +++++++++++++++++++++++++++++++
> >  drivers/gpu/drm/vc4/vc4_drv.c     |  2 ++
> >  drivers/gpu/drm/vc4/vc4_drv.h     |  2 ++
> >  drivers/gpu/drm/vc4/vc4_kms.c     |  6 +++-
> >  4 files changed, 67 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/gpu/drm/vc4/vc4_debugfs.c b/drivers/gpu/drm/vc4/vc4_debugfs.c
> > index 7a0003de71ab..8f4d7fadb226 100644
> > --- a/drivers/gpu/drm/vc4/vc4_debugfs.c
> > +++ b/drivers/gpu/drm/vc4/vc4_debugfs.c
> > @@ -32,9 +32,67 @@ static const struct drm_info_list vc4_debugfs_list[] = {
> >  
> >  #define VC4_DEBUGFS_ENTRIES ARRAY_SIZE(vc4_debugfs_list)
> >  
> > +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);
> > +}
> > +
> > +static 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,
> > +};
> > +
> >  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;
> 
> Hm, maybe you could use debugfs_create_bool() instead of
> re-implementing it. The values won't be enabled/disabled though
> (IIRC, it's Y or N).

Oh, I didn't know about that! It definitely makes more sense yes.

Thanks,

Paul

> > +
> >  	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..12ac971d24d6 100644
> > --- a/drivers/gpu/drm/vc4/vc4_drv.c
> > +++ b/drivers/gpu/drm/vc4/vc4_drv.c
> > @@ -290,6 +290,8 @@ 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..8d0f2f16a9e8 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;
> >  
> > 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 = {