Message-ID: <20170706075313.bn2exiklfabgc25t@phenom.ffwll.local>
Date:   Thu, 6 Jul 2017 09:53:13 +0200
From:   Daniel Vetter <daniel@...ll.ch>
To:     Keith Packard <keithp@...thp.com>
Cc:     linux-kernel@...r.kernel.org, Dave Airlie <airlied@...hat.com>,
        Daniel Vetter <daniel@...ll.ch>,
        dri-devel@...ts.freedesktop.org
Subject: Re: [PATCH 3/3] drm: Add CRTC_GET_SEQUENCE and CRTC_QUEUE_SEQUENCE
 ioctls

On Wed, Jul 05, 2017 at 03:10:13PM -0700, Keith Packard wrote:
> These provide crtc-id based functions instead of pipe-number, while
> also offering higher resolution time (ns) and wider frame count (64)
> as required by the Vulkan API.
> 
> Signed-off-by: Keith Packard <keithp@...thp.com>

I very much like this since the old ioctl really is a rather bad horror
show. And since it's tied in with ums drivers everything is complicated.

\o/ for much cleaner ioctls.

Bunch of comments below, but looks good overall.
-Daniel

> ---
>  drivers/gpu/drm/drm_internal.h |   6 ++
>  drivers/gpu/drm/drm_ioctl.c    |   2 +
>  drivers/gpu/drm/drm_vblank.c   | 148 +++++++++++++++++++++++++++++++++++++++++
>  include/drm/drm_vblank.h       |   1 +
>  include/uapi/drm/drm.h         |  32 +++++++++
>  5 files changed, 189 insertions(+)
> 
> diff --git a/drivers/gpu/drm/drm_internal.h b/drivers/gpu/drm/drm_internal.h
> index 5cecc974d2f9..b68a193b7907 100644
> --- a/drivers/gpu/drm/drm_internal.h
> +++ b/drivers/gpu/drm/drm_internal.h
> @@ -65,6 +65,12 @@ int drm_legacy_irq_control(struct drm_device *dev, void *data,
>  int drm_legacy_modeset_ctl(struct drm_device *dev, void *data,
>  			   struct drm_file *file_priv);
>  
> +int drm_crtc_get_sequence_ioctl(struct drm_device *dev, void *data,
> +				struct drm_file *filp);
> +
> +int drm_crtc_queue_sequence_ioctl(struct drm_device *dev, void *data,
> +				  struct drm_file *filp);
> +
>  /* drm_auth.c */
>  int drm_getmagic(struct drm_device *dev, void *data,
>  		 struct drm_file *file_priv);
> diff --git a/drivers/gpu/drm/drm_ioctl.c b/drivers/gpu/drm/drm_ioctl.c
> index f1e568176da9..63016cf3e224 100644
> --- a/drivers/gpu/drm/drm_ioctl.c
> +++ b/drivers/gpu/drm/drm_ioctl.c
> @@ -657,6 +657,8 @@ static const struct drm_ioctl_desc drm_ioctls[] = {
>  		      DRM_UNLOCKED|DRM_RENDER_ALLOW),
>  	DRM_IOCTL_DEF(DRM_IOCTL_SYNCOBJ_FD_TO_HANDLE, drm_syncobj_fd_to_handle_ioctl,
>  		      DRM_UNLOCKED|DRM_RENDER_ALLOW),
> +	DRM_IOCTL_DEF(DRM_IOCTL_CRTC_GET_SEQUENCE, drm_crtc_get_sequence_ioctl, DRM_UNLOCKED),
> +	DRM_IOCTL_DEF(DRM_IOCTL_CRTC_QUEUE_SEQUENCE, drm_crtc_queue_sequence_ioctl, DRM_UNLOCKED),

I started a discussion a while back whether these should be restricted to
DRM_MASTER (i.e. the modeset resource owner) or available to everyone.
Since it's read-only I guess we can keep it accessible to everyone, but it
has a bit the problem that client app developers see this, think it does
what it does and then use it to schedule frames without asking the
compositor. Which sometimes even works, but isn't really proper design.
The reasons seems to be that on X11 there's no EGL extension for accurate
timing frame updates (DRI2/3 can do it ofc, and glx exposes it, but glx is
uncool or something like that).

>  };
>  
>  #define DRM_CORE_IOCTL_COUNT	ARRAY_SIZE( drm_ioctls )
> diff --git a/drivers/gpu/drm/drm_vblank.c b/drivers/gpu/drm/drm_vblank.c
> index 9ae170857ef6..93004b1bf84c 100644
> --- a/drivers/gpu/drm/drm_vblank.c
> +++ b/drivers/gpu/drm/drm_vblank.c
> @@ -817,6 +817,12 @@ static void send_vblank_event(struct drm_device *dev,
>  			e->event.vbl.tv_usec = now->tv_nsec / 1000;
>  		}
>  		break;
> +	case DRM_EVENT_CRTC_SEQUENCE:
> +		if (seq)
> +			e->event.seq.sequence = seq;
> +		if (now)
> +			e->event.seq.time_ns = timespec_to_ns(now);
> +		break;
>  	}
>  	trace_drm_vblank_event_delivered(e->base.file_priv, e->pipe, seq);
>  	drm_send_event_locked(dev, &e->base);
> @@ -1516,6 +1522,7 @@ int drm_wait_vblank(struct drm_device *dev, void *data,
>  		DRM_DEBUG("crtc %d failed to acquire vblank counter, %d\n", pipe, ret);
>  		return ret;
>  	}
> +
>  	seq = drm_vblank_count(dev, pipe);
>  
>  	switch (vblwait->request.type & _DRM_VBLANK_TYPES_MASK) {
> @@ -1676,3 +1683,144 @@ bool drm_crtc_handle_vblank(struct drm_crtc *crtc)
>  	return drm_handle_vblank(crtc->dev, drm_crtc_index(crtc));
>  }
>  EXPORT_SYMBOL(drm_crtc_handle_vblank);
> +
> +/*
> + * Get crtc VBLANK count.
> + *
> + * \param dev DRM device
> + * \param data user arguement, pointing to a drm_crtc_get_sequence structure.
> + * \param file_priv drm file private for the user's open file descriptor
> + */

Since this stuff isn't parsed by kerneldoc I tend to just free-form ioctl
comments completely. Someday maybe someone even gets around to doing
proper uabi documentation :-) Just an aside.
> +
> +int drm_crtc_get_sequence_ioctl(struct drm_device *dev, void *data,
> +				struct drm_file *file_priv)
> +{
> +	struct drm_crtc *crtc;
> +	int pipe;
> +	struct drm_crtc_get_sequence *get_seq = data;
> +	struct timespec now;
> +

You need a DRIVER_MODESET check here or the drm_crtc_find will oops. Same
below.

> +	if (!dev->irq_enabled)
> +		return -EINVAL;
> +
> +	crtc = drm_crtc_find(dev, get_seq->crtc_id);
> +	if (!crtc)
> +		return -ENOENT;
> +
> +	pipe = drm_crtc_index(crtc);
> +
> +	get_seq->sequence = drm_vblank_count_and_time(dev, pipe, &now);

This can give you and old vblank if the vblank is off (i.e. sw state
hasn't be regularly updated). I think we want a new
drm_crtc_accurate_vblank_count_and_time variant.

Another thing that is very ill-defined in the old vblank ioctl and that we
could fix here: Asking for vblanks when the CRTC is off is a bit silly.
Asking for the sequence when it's off makes some sense, but might still be
good to give userspace some indication in the new struct? This also from
the pov of the unpriviledge vblank waiter use-case that I wondered about
earlier.

> +	get_seq->sequence_ns = timespec_to_ns(&now);
> +	return 0;
> +}
> +
> +/*
> + * Queue a event for VBLANK sequence
> + *
> + * \param dev DRM device
> + * \param data user arguement, pointing to a drm_crtc_queue_sequence structure.
> + * \param file_priv drm file private for the user's open file descriptor
> + */
> +
> +int drm_crtc_queue_sequence_ioctl(struct drm_device *dev, void *data,
> +				  struct drm_file *file_priv)
> +{
> +	struct drm_crtc *crtc;
> +	struct drm_vblank_crtc *vblank;
> +	int pipe;
> +	struct drm_crtc_queue_sequence *queue_seq = data;
> +	struct timespec now;
> +	struct drm_pending_vblank_event *e;
> +	u32 flags;
> +	u64 seq;
> +	u64 req_seq;
> +	int ret;
> +	unsigned long spin_flags;
> +
> +	if (!dev->irq_enabled)
> +		return -EINVAL;
> +
> +	crtc = drm_crtc_find(dev, queue_seq->crtc_id);
> +	if (!crtc)
> +		return -ENOENT;
> +
> +	flags = queue_seq->flags;
> +	/* Check valid flag bits */
> +	if (flags & ~(DRM_CRTC_SEQUENCE_RELATIVE|
> +		      DRM_CRTC_SEQUENCE_NEXT_ON_MISS|
> +		      DRM_CRTC_SEQUENCE_FIRST_PIXEL_OUT))
> +		return -EINVAL;
> +
> +	/* Check for valid signal edge */
> +	if (!(flags & DRM_CRTC_SEQUENCE_FIRST_PIXEL_OUT))
> +		return -EINVAL;

This seems new, maybe drop it until we need it?

> +
> +	pipe = drm_crtc_index(crtc);
> +
> +	vblank = &dev->vblank[pipe];
> +
> +	e = kzalloc(sizeof(*e), GFP_KERNEL);
> +	if (e == NULL)
> +		return -ENOMEM;
> +
> +	ret = drm_vblank_get(dev, pipe);

drm_crtc_vblank_get pls, would be sweet if we can avoid the (dev, pipe)
pairs as much as possible. Same for all the others.

> +	if (ret) {
> +		DRM_DEBUG("crtc %d failed to acquire vblank counter, %d\n", pipe, ret);
> +		goto err_free;
> +	}
> +
> +	seq = drm_vblank_count_and_time(dev, pipe, &now);

I think here there's no need for the accurate version, since we
force-enable the vblanks already.

> +	req_seq = queue_seq->sequence;
> +
> +	if (flags & DRM_CRTC_SEQUENCE_RELATIVE)
> +		req_seq += seq;
> +
> +	if ((flags & DRM_CRTC_SEQUENCE_NEXT_ON_MISS) && vblank_passed(seq, req_seq))
> +		req_seq = seq + 1;
> +
> +	e->pipe = pipe;
> +	e->event.base.type = DRM_EVENT_CRTC_SEQUENCE;
> +	e->event.base.length = sizeof(e->event.seq);
> +	e->event.seq.user_data = queue_seq->user_data;

No need for crtc_id in this event? Or do we expect userspace to encode
that in the user_data somehow? I don't think it's a real problem since
we'll only deliver one event per request, so clear for which crtc it is.
In atomic we might deliver multiple events (one for each crtc) so that's
why it's needed there.

But might be useful just for consistency.

> +
> +	spin_lock_irqsave(&dev->event_lock, spin_flags);
> +
> +	/*
> +	 * drm_crtc_vblank_off() might have been called after we called
> +	 * drm_vblank_get(). drm_crtc_vblank_off() holds event_lock around the
> +	 * vblank disable, so no need for further locking.  The reference from
> +	 * drm_vblank_get() protects against vblank disable from another source.
> +	 */
> +	if (!READ_ONCE(vblank->enabled)) {
> +		ret = -EINVAL;
> +		goto err_unlock;
> +	}
> +
> +	ret = drm_event_reserve_init_locked(dev, file_priv, &e->base,
> +					    &e->event.base);
> +
> +	if (ret)
> +		goto err_unlock;
> +
> +	e->sequence = req_seq;
> +
> +	if (vblank_passed(seq, req_seq)) {
> +		drm_vblank_put(dev, pipe);
> +		send_vblank_event(dev, e, seq, &now);
> +		queue_seq->sequence = seq;
> +	} else {
> +		/* drm_handle_vblank_events will call drm_vblank_put */
> +		list_add_tail(&e->base.link, &dev->vblank_event_list);
> +		queue_seq->sequence = req_seq;
> +	}
> +
> +	spin_unlock_irqrestore(&dev->event_lock, spin_flags);
> +	return 0;
> +
> +err_unlock:
> +	spin_unlock_irqrestore(&dev->event_lock, spin_flags);
> +	drm_vblank_put(dev, pipe);
> +err_free:
> +	kfree(e);
> +	return ret;
> +}
> diff --git a/include/drm/drm_vblank.h b/include/drm/drm_vblank.h
> index 3ef7ddc5db5f..8a5e1dfe3be7 100644
> --- a/include/drm/drm_vblank.h
> +++ b/include/drm/drm_vblank.h
> @@ -57,6 +57,7 @@ struct drm_pending_vblank_event {
>  	union {
>  		struct drm_event base;
>  		struct drm_event_vblank vbl;
> +		struct drm_event_crtc_sequence seq;
>  	} event;
>  };
>  
> diff --git a/include/uapi/drm/drm.h b/include/uapi/drm/drm.h
> index 101593ab10ac..dc16d42a88c7 100644
> --- a/include/uapi/drm/drm.h
> +++ b/include/uapi/drm/drm.h
> @@ -718,6 +718,27 @@ struct drm_syncobj_handle {
>  	__u32 pad;
>  };
>  
> +/* Query current scanout sequence number */
> +struct drm_crtc_get_sequence {
> +	__u32 crtc_id;
> +	__u32 pad;
> +	__u64 sequence;
> +	__u64 sequence_ns;
> +};
> +
> +/* Queue event to be delivered at specified sequence */
> +
> +#define DRM_CRTC_SEQUENCE_RELATIVE		0x00000001	/* sequence is relative to current */
> +#define DRM_CRTC_SEQUENCE_NEXT_ON_MISS		0x00000002	/* Use next sequence if we've missed */
> +#define DRM_CRTC_SEQUENCE_FIRST_PIXEL_OUT	0x00000004	/* Signal when first pixel is displayed */

I thought this is already the semantics our current vblank events have (in
the timestamp, when exactly the event comes out isn't defined further than
"somewhere around vblank"). Since it's unsed I'd just remove this #define.

> +
> +struct drm_crtc_queue_sequence {
> +	__u32 crtc_id;
> +	__u32 flags;
> +	__u64 sequence;		/* on input, target sequence. on output, actual sequence */
> +	__u64 user_data;	/* user data passed to event */
> +};

In both ioctl handlers pls make sure everything you don't look at is 0,
including unused stuff like pad. Otherwise userspace might fail to clear
them, and we can never use them in the future. Maybe just rename pad to
flags right away.

> +
>  #if defined(__cplusplus)
>  }
>  #endif
> @@ -800,6 +821,9 @@ extern "C" {
>  
>  #define DRM_IOCTL_WAIT_VBLANK		DRM_IOWR(0x3a, union drm_wait_vblank)
>  
> +#define DRM_IOCTL_CRTC_GET_SEQUENCE	DRM_IOWR(0x3b, struct drm_crtc_get_sequence)
> +#define DRM_IOCTL_CRTC_QUEUE_SEQUENCE	DRM_IOWR(0x3c, struct drm_crtc_queue_sequence)
> +
>  #define DRM_IOCTL_UPDATE_DRAW		DRM_IOW(0x3f, struct drm_update_draw)
>  
>  #define DRM_IOCTL_MODE_GETRESOURCES	DRM_IOWR(0xA0, struct drm_mode_card_res)
> @@ -871,6 +895,7 @@ struct drm_event {
>  
>  #define DRM_EVENT_VBLANK 0x01
>  #define DRM_EVENT_FLIP_COMPLETE 0x02
> +#define DRM_EVENT_CRTC_SEQUENCE	0x03
>  
>  struct drm_event_vblank {
>  	struct drm_event base;
> @@ -881,6 +906,13 @@ struct drm_event_vblank {
>  	__u32 crtc_id; /* 0 on older kernels that do not support this */
>  };
>  
> +struct drm_event_crtc_sequence {
> +	struct drm_event	base;
> +	__u64			user_data;
> +	__u64			time_ns;
> +	__u64			sequence;
> +};
> +
>  /* typedef area */
>  #ifndef __KERNEL__
>  typedef struct drm_clip_rect drm_clip_rect_t;
> -- 
> 2.11.0
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch

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