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Subject: Re: [RFC] drm/atomic+msm: add helper to implement legacy dirtyfb
To:     Rob Clark <robdclark@gmail.com>, dri-devel@lists.freedesktop.org
Cc:     David Airlie <airlied@linux.ie>, linux-arm-msm@vger.kernel.org,
        linux-kernel@vger.kernel.org,
        Deepak Singh Rawat <drawat@vmware.com>,
        freedreno@lists.freedesktop.org,
        Lukasz Spintzyk <lukasz.spintzyk@displaylink.com>
References: <20180403224225.26776-1-robdclark@gmail.com>
From:   =?UTF-8?Q?Noralf_Tr=c3=b8nnes?= <noralf@tronnes.org>
Message-ID: <4dac69b7-b0e6-a014-1c36-1a9934f14120@tronnes.org>
Date:   Wed, 4 Apr 2018 19:41:43 +0200
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Den 04.04.2018 00.42, skrev Rob Clark:
> Add an atomic helper to implement dirtyfb support.  This is needed to
> support DSI command-mode panels with x11 userspace (ie. when we can't
> rely on pageflips to trigger a flush to the panel).
>
> To signal to the driver that the async atomic update needs to
> synchronize with fences, even though the fb didn't change, the
> drm_atomic_state::dirty flag is added.
>
> Signed-off-by: Rob Clark <robdclark@gmail.com>
> ---
> Background: there are a number of different folks working on getting
> upstream kernel working on various different phones/tablets with qcom
> SoC's.. many of them have command mode panels, so we kind of need a
> way to support the legacy dirtyfb ioctl for x11 support.
>
> I know there is work on a proprer non-legacy atomic property for
> userspace to communicate dirty-rect(s) to the kernel, so this can
> be improved from triggering a full-frame flush once that is in
> place.  But we kinda needa a stop-gap solution.
>
> I had considered an in-driver solution for this, but things get a
> bit tricky if userspace ands up combining dirtyfb ioctls with page-
> flips, because we need to synchronize setting various CTL.FLUSH bits
> with setting the CTL.START bit.  (ie. really all we need to do for
> cmd mode panels is bang CTL.START, but is this ends up racing with
> pageflips setting FLUSH bits, then bad things.)  The easiest soln
> is to wrap this up as an atomic commit and rely on the worker to
> serialize things.  Hence adding an atomic dirtyfb helper.
>
> I guess at least the helper, with some small addition to translate
> and pass-thru the dirty rect(s) is useful to the final atomic dirty-
> rect property solution.  Depending on how far off that is, a stop-
> gap solution could be useful.

I have been waiting for someone to address this since I'm not skilled
enough myself to tackle the atomic machinery. It would be be nice to do
all flushing during commit since that would mean that the tinydrm drivers
could be driven solely through drm_simple_display_pipe_funcs. I wouldn't
have to wire through the dirty callback like I do now.

I see that you use a nonblocking commit. What happens if a new dirtyfb
comes in before the previous is done?

If we could save the dirty clips, then I could use this in tinydrm.
A full flush over SPI takes ~50ms so I need to shave off where I can.

This works for me in my tinydrm world:

diff --git a/include/drm/drm_plane.h b/include/drm/drm_plane.h
index c64225274807..218cb36757fa 100644
--- a/include/drm/drm_plane.h
+++ b/include/drm/drm_plane.h
@@ -28,6 +28,7 @@
  #include <drm/drm_mode_object.h>
  #include <drm/drm_color_mgmt.h>

+struct drm_clip_rect;
  struct drm_crtc;
  struct drm_printer;
  struct drm_modeset_acquire_ctx;
@@ -85,6 +86,9 @@ struct drm_plane_state {
          */
         bool dirty;

+       struct drm_clip_rect *dirty_clips;
+       unsigned int num_dirty_clips;
+
         /**
          * @fence:
          *
diff --git a/drivers/gpu/drm/drm_atomic_helper.c 
b/drivers/gpu/drm/drm_atomic_helper.c
index 8066c508ab50..e00b8247b7c5 100644
--- a/drivers/gpu/drm/drm_atomic_helper.c
+++ b/drivers/gpu/drm/drm_atomic_helper.c
@@ -3521,6 +3521,8 @@ void 
__drm_atomic_helper_plane_duplicate_state(struct drm_plane *plane,
                 drm_framebuffer_get(state->fb);

         state->dirty = false;
+       state->dirty_clips = NULL;
+       state->num_dirty_clips = 0;
         state->fence = NULL;
         state->commit = NULL;
  }
@@ -3567,6 +3569,8 @@ void 
__drm_atomic_helper_plane_destroy_state(struct drm_plane_state *state)

         if (state->commit)
                 drm_crtc_commit_put(state->commit);
+
+       kfree(state->dirty_clips);
  }
  EXPORT_SYMBOL(__drm_atomic_helper_plane_destroy_state);

@@ -3877,8 +3881,20 @@ int drm_atomic_helper_dirtyfb(struct 
drm_framebuffer *fb,
         struct drm_modeset_acquire_ctx ctx;
         struct drm_atomic_state *state;
         struct drm_plane *plane;
+       bool fb_found = false;
         int ret = 0;

+       /* fbdev can flush even when we don't want it to */
+       drm_for_each_plane(plane, fb->dev) {
+               if (plane->state->fb == fb) {
+                       fb_found = true;
+                       break;
+               }
+       }
+
+       if (!fb_found)
+               return 0;
+
         /*
          * When called from ioctl, we are interruptable, but not when
          * called internally (ie. defio worker)
@@ -3907,6 +3923,25 @@ int drm_atomic_helper_dirtyfb(struct 
drm_framebuffer *fb,
                 }

                 plane_state->dirty = true;
+               if (clips && num_clips)
+                       plane_state->dirty_clips = kmemdup(clips, 
num_clips * sizeof(*clips),
+ GFP_KERNEL);
+               else
+                       plane_state->dirty_clips = 
kzalloc(sizeof(*clips), GFP_KERNEL);
+
+               if (!plane_state->dirty_clips) {
+                       ret = -ENOMEM;
+                       goto out;
+               }
+
+               if (clips && num_clips) {
+                       plane_state->num_dirty_clips = num_clips;
+               } else {
+                       /* TODO: Maybe choose better max values */
+                       plane_state->dirty_clips->x2 = ~0;
+                       plane_state->dirty_clips->y2 = ~0;
+                       plane_state->num_dirty_clips = 1;
+               }
         }

         ret = drm_atomic_nonblocking_commit(state);
diff --git a/drivers/gpu/drm/tinydrm/core/tinydrm-pipe.c 
b/drivers/gpu/drm/tinydrm/core/tinydrm-pipe.c
index e68b528ae64d..1a0c72c496f6 100644
--- a/drivers/gpu/drm/tinydrm/core/tinydrm-pipe.c
+++ b/drivers/gpu/drm/tinydrm/core/tinydrm-pipe.c
@@ -121,12 +121,14 @@ void tinydrm_display_pipe_update(struct 
drm_simple_display_pipe *pipe,
                                  struct drm_plane_state *old_state)
  {
         struct tinydrm_device *tdev = pipe_to_tinydrm(pipe);
-       struct drm_framebuffer *fb = pipe->plane.state->fb;
+       struct drm_plane_state *new_state = pipe->plane.state;
+       struct drm_framebuffer *fb = new_state->fb;
         struct drm_crtc *crtc = &tdev->pipe.crtc;

-       if (fb && (fb != old_state->fb)) {
+       if (fb && ((fb != old_state->fb) || new_state->dirty_clips)) {
                 if (tdev->fb_dirty)
-                       tdev->fb_dirty(fb, NULL, 0, 0, NULL, 0);
+                       tdev->fb_dirty(fb, NULL, 0, 0, 
new_state->dirty_clips,
+ new_state->num_dirty_clips);
         }

         if (crtc->state->event) {
diff --git a/drivers/gpu/drm/tinydrm/mipi-dbi.c 
b/drivers/gpu/drm/tinydrm/mipi-dbi.c
index 4d1fb31a781f..49dee24dde60 100644
--- a/drivers/gpu/drm/tinydrm/mipi-dbi.c
+++ b/drivers/gpu/drm/tinydrm/mipi-dbi.c
@@ -9,6 +9,7 @@
   * (at your option) any later version.
   */

+#include <drm/drm_atomic_helper.h>
  #include <drm/drm_gem_framebuffer_helper.h>
  #include <drm/tinydrm/mipi-dbi.h>
  #include <drm/tinydrm/tinydrm-helpers.h>
@@ -254,7 +257,7 @@ static int mipi_dbi_fb_dirty(struct drm_framebuffer *fb,
  static const struct drm_framebuffer_funcs mipi_dbi_fb_funcs = {
         .destroy        = drm_gem_fb_destroy,
         .create_handle  = drm_gem_fb_create_handle,
-       .dirty          = tinydrm_fb_dirty,
+       .dirty          = drm_atomic_helper_dirtyfb,
  };

  /**


I did some brief testing a few months back with PRIME buffers imported
from vc4 and it looked like X11 sometimes did a page flip followed by a
dirtyfb. This kills performance for me since I flush on both. Do you know
any details on how/where X11 handles this?

Noralf.

>   drivers/gpu/drm/drm_atomic_helper.c | 66 +++++++++++++++++++++++++++++++++++++
>   drivers/gpu/drm/msm/msm_atomic.c    |  5 ++-
>   drivers/gpu/drm/msm/msm_fb.c        |  1 +
>   include/drm/drm_atomic_helper.h     |  4 +++
>   include/drm/drm_plane.h             |  9 +++++
>   5 files changed, 84 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c
> index c35654591c12..a578dc681b27 100644
> --- a/drivers/gpu/drm/drm_atomic_helper.c
> +++ b/drivers/gpu/drm/drm_atomic_helper.c
> @@ -3504,6 +3504,7 @@ void __drm_atomic_helper_plane_duplicate_state(struct drm_plane *plane,
>   	if (state->fb)
>   		drm_framebuffer_get(state->fb);
>   
> +	state->dirty = false;
>   	state->fence = NULL;
>   	state->commit = NULL;
>   }
> @@ -3847,6 +3848,71 @@ int drm_atomic_helper_legacy_gamma_set(struct drm_crtc *crtc,
>   }
>   EXPORT_SYMBOL(drm_atomic_helper_legacy_gamma_set);
>   
> +/**
> + * drm_atomic_helper_dirtyfb - helper for dirtyfb
> + *
> + * A helper to implement drm_framebuffer_funcs::dirty
> + */
> +int drm_atomic_helper_dirtyfb(struct drm_framebuffer *fb,
> +			      struct drm_file *file_priv, unsigned flags,
> +			      unsigned color, struct drm_clip_rect *clips,
> +			      unsigned num_clips)
> +{
> +	struct drm_modeset_acquire_ctx ctx;
> +	struct drm_atomic_state *state;
> +	struct drm_plane *plane;
> +	int ret = 0;
> +
> +	/*
> +	 * When called from ioctl, we are interruptable, but not when
> +	 * called internally (ie. defio worker)
> +	 */
> +	drm_modeset_acquire_init(&ctx,
> +		file_priv ? DRM_MODESET_ACQUIRE_INTERRUPTIBLE : 0);
> +
> +	state = drm_atomic_state_alloc(fb->dev);
> +	if (!state) {
> +		ret = -ENOMEM;
> +		goto out;
> +	}
> +	state->acquire_ctx = &ctx;
> +
> +retry:
> +	drm_for_each_plane(plane, fb->dev) {
> +		struct drm_plane_state *plane_state;
> +
> +		if (plane->state->fb != fb)
> +			continue;
> +
> +		plane_state = drm_atomic_get_plane_state(state, plane);
> +		if (IS_ERR(plane_state)) {
> +			ret = PTR_ERR(plane_state);
> +			goto out;
> +		}
> +
> +		plane_state->dirty = true;
> +	}
> +
> +	ret = drm_atomic_nonblocking_commit(state);
> +
> +out:
> +	if (ret == -EDEADLK) {
> +		drm_atomic_state_clear(state);
> +		ret = drm_modeset_backoff(&ctx);
> +		if (!ret)
> +			goto retry;
> +	}
> +
> +	drm_atomic_state_put(state);
> +
> +	drm_modeset_drop_locks(&ctx);
> +	drm_modeset_acquire_fini(&ctx);
> +
> +	return ret;
> +
> +}
> +EXPORT_SYMBOL(drm_atomic_helper_dirtyfb);
> +
>   /**
>    * __drm_atomic_helper_private_duplicate_state - copy atomic private state
>    * @obj: CRTC object
> diff --git a/drivers/gpu/drm/msm/msm_atomic.c b/drivers/gpu/drm/msm/msm_atomic.c
> index bf5f8c39f34d..bb55a048e98b 100644
> --- a/drivers/gpu/drm/msm/msm_atomic.c
> +++ b/drivers/gpu/drm/msm/msm_atomic.c
> @@ -201,7 +201,10 @@ int msm_atomic_commit(struct drm_device *dev,
>   	 * Figure out what fence to wait for:
>   	 */
>   	for_each_oldnew_plane_in_state(state, plane, old_plane_state, new_plane_state, i) {
> -		if ((new_plane_state->fb != old_plane_state->fb) && new_plane_state->fb) {
> +		bool sync_fb = new_plane_state->fb &&
> +			((new_plane_state->fb != old_plane_state->fb) ||
> +			 new_plane_state->dirty);
> +		if (sync_fb) {
>   			struct drm_gem_object *obj = msm_framebuffer_bo(new_plane_state->fb, 0);
>   			struct msm_gem_object *msm_obj = to_msm_bo(obj);
>   			struct dma_fence *fence = reservation_object_get_excl_rcu(msm_obj->resv);
> diff --git a/drivers/gpu/drm/msm/msm_fb.c b/drivers/gpu/drm/msm/msm_fb.c
> index 0e0c87252ab0..a5d882a34a33 100644
> --- a/drivers/gpu/drm/msm/msm_fb.c
> +++ b/drivers/gpu/drm/msm/msm_fb.c
> @@ -62,6 +62,7 @@ static void msm_framebuffer_destroy(struct drm_framebuffer *fb)
>   static const struct drm_framebuffer_funcs msm_framebuffer_funcs = {
>   	.create_handle = msm_framebuffer_create_handle,
>   	.destroy = msm_framebuffer_destroy,
> +	.dirty = drm_atomic_helper_dirtyfb,
>   };
>   
>   #ifdef CONFIG_DEBUG_FS
> diff --git a/include/drm/drm_atomic_helper.h b/include/drm/drm_atomic_helper.h
> index 26aaba58d6ce..9b7a95c2643d 100644
> --- a/include/drm/drm_atomic_helper.h
> +++ b/include/drm/drm_atomic_helper.h
> @@ -183,6 +183,10 @@ int drm_atomic_helper_legacy_gamma_set(struct drm_crtc *crtc,
>   				       u16 *red, u16 *green, u16 *blue,
>   				       uint32_t size,
>   				       struct drm_modeset_acquire_ctx *ctx);
> +int drm_atomic_helper_dirtyfb(struct drm_framebuffer *fb,
> +			      struct drm_file *file_priv, unsigned flags,
> +			      unsigned color, struct drm_clip_rect *clips,
> +			      unsigned num_clips);
>   void __drm_atomic_helper_private_obj_duplicate_state(struct drm_private_obj *obj,
>   						     struct drm_private_state *state);
>   
> diff --git a/include/drm/drm_plane.h b/include/drm/drm_plane.h
> index f7bf4a48b1c3..296fa22bda7a 100644
> --- a/include/drm/drm_plane.h
> +++ b/include/drm/drm_plane.h
> @@ -76,6 +76,15 @@ struct drm_plane_state {
>   	 */
>   	struct drm_framebuffer *fb;
>   
> +	/**
> +	 * @dirty:
> +	 *
> +	 * Flag that indicates the fb contents have changed even though the
> +	 * fb has not.  This is mostly a stop-gap solution until we have
> +	 * atomic dirty-rect(s) property.
> +	 */
> +	bool dirty;
> +
>   	/**
>   	 * @fence:
>   	 *