Re: [PATCH v6 6/6] drm/i915/skl: Update DDB values atomically with wms/plane attrs

Lyude Paul
2016-08-03T21:39:23Z

On Wed, 2016-08-03 at 18:00 +0300, Ville Syrjälä wrote:
> On Tue, Aug 02, 2016 at 06:37:37PM -0400, Lyude wrote:
> >
> > Now that we can hook into update_crtcs and control the order in which we
> > update CRTCs at each modeset, we can finish the final step of fixing
> > Skylake's watermark handling by performing DDB updates at the same time
> > as plane updates and watermark updates.
> >
> > The first major change in this patch is skl_update_crtcs(), which
> > handles ensuring that we order each CRTC update in our atomic commits
> > properly so that they honor the DDB flush order.
> >
> > The second major change in this patch is the order in which we flush the
> > pipes. While the previous order may have worked, it can't be used in
> > this approach since it no longer will do the right thing. For example,
> > using the old ddb flush order:
> >
> > We have pipes A, B, and C enabled, and we're disabling C. Initial ddb
> > allocation looks like this:
> >
> > >
> > >   A   |   B   |xxxxxxx|
> >
> > Since we're performing the ddb updates after performing any CRTC
> > disablements in intel_atomic_commit_tail(), the space to the right of
> > pipe B is unallocated.
> >
> > 1. Flush pipes with new allocation contained into old space. None
> >    apply, so we skip this
> > 2. Flush pipes having their allocation reduced, but overlapping with a
> >    previous allocation. None apply, so we also skip this
> > 3. Flush pipes that got more space allocated. This applies to A and B,
> >    giving us the following update order: A, B
> >
> > This is wrong, since updating pipe A first will cause it to overlap with
> > B and potentially burst into flames. Our new order (see the code
> > comments for details) would update the pipes in the proper order: B, A.
> >
> > As well, we calculate the order for each DDB update during the check
> > phase, and reference it later in the commit phase when we hit
> > skl_update_crtcs().
> >
> > This long overdue patch fixes the rest of the underruns on Skylake.
> >
> > Changes since v1:
> >  - Add skl_ddb_entry_write() for cursor into skl_write_cursor_wm()
> >
> > Fixes: 0e8fb7ba7ca5 ("drm/i915/skl: Flush the WM configuration")
> > Fixes: 8211bd5bdf5e ("drm/i915/skl: Program the DDB allocation")
> > Signed-off-by: Lyude <cpaul@redhat.com>
> > [omitting CC for stable, since this patch will need to be changed for
> > such backports first]
> > Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
> > Cc: Daniel Vetter <daniel.vetter@intel.com>
> > Cc: Radhakrishna Sripada <radhakrishna.sripada@intel.com>
> > Cc: Hans de Goede <hdegoede@redhat.com>
> > Cc: Matt Roper <matthew.d.roper@intel.com>
> > ---
> >  drivers/gpu/drm/i915/intel_display.c | 100 ++++++++++--
> >  drivers/gpu/drm/i915/intel_drv.h     |  10 ++
> >  drivers/gpu/drm/i915/intel_pm.c      | 288 ++++++++++++++++--------------
> > -----
> >  3 files changed, 233 insertions(+), 165 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/i915/intel_display.c
> > b/drivers/gpu/drm/i915/intel_display.c
> > index 59cf513..06295f7 100644
> > --- a/drivers/gpu/drm/i915/intel_display.c
> > +++ b/drivers/gpu/drm/i915/intel_display.c
> > @@ -12897,16 +12897,23 @@ static void verify_wm_state(struct drm_crtc *crtc,
> >     hw_entry->start, hw_entry->end);
> >   }
> >
> > - /* cursor */
> > - hw_entry = &hw_ddb.plane[pipe][PLANE_CURSOR];
> > - sw_entry = &sw_ddb->plane[pipe][PLANE_CURSOR];
> > -
> > - if (!skl_ddb_entry_equal(hw_entry, sw_entry)) {
> > - DRM_ERROR("mismatch in DDB state pipe %c cursor "
> > -   "(expected (%u,%u), found (%u,%u))\n",
> > -   pipe_name(pipe),
> > -   sw_entry->start, sw_entry->end,
> > -   hw_entry->start, hw_entry->end);
> > + /*
> > +  * cursor
> > +  * If the cursor plane isn't active, we may not have updated it's
> > ddb
> > +  * allocation. In that case since the ddb allocation will be
> > updated
> > +  * once the plane becomes visible, we can skip this check
> > +  */
> > + if (intel_crtc->cursor_addr) {
> > + hw_entry = &hw_ddb.plane[pipe][PLANE_CURSOR];
> > + sw_entry = &sw_ddb->plane[pipe][PLANE_CURSOR];
> > +
> > + if (!skl_ddb_entry_equal(hw_entry, sw_entry)) {
> > + DRM_ERROR("mismatch in DDB state pipe %c cursor "
> > +   "(expected (%u,%u), found (%u,%u))\n",
> > +   pipe_name(pipe),
> > +   sw_entry->start, sw_entry->end,
> > +   hw_entry->start, hw_entry->end);
> > + }
> >   }
> >  }
> >
> > @@ -13658,6 +13665,72 @@ static void intel_update_crtcs(struct
> > drm_atomic_state *state,
> >   }
> >  }
> >
> > +static inline void
> > +skl_do_ddb_step(struct drm_atomic_state *state,
> > + enum skl_ddb_step step)
> > +{
> > + struct intel_atomic_state *intel_state =
> > to_intel_atomic_state(state);
> > + struct drm_crtc *crtc;
> > + struct drm_crtc_state *old_crtc_state;
> > + unsigned int crtc_vblank_mask; /* unused */
> > + int i;
> > +
> > + for_each_crtc_in_state(state, crtc, old_crtc_state, i) {
> > + struct intel_crtc *intel_crtc = to_intel_crtc(crtc);
> > + struct intel_crtc_state *cstate =
> > + to_intel_crtc_state(crtc->state);
> > + bool vblank_wait = false;
> > +
> > + if (cstate->wm.skl.ddb_realloc != step || !crtc->state-
> > >active)
> > + continue;
> > +
> > + /*
> > +  * If we're changing the ddb allocation of this pipe to
> > make
> > +  * room for another pipe, we have to wait for the pipe's
> > ddb
> > +  * allocations to actually update by waiting for a vblank.
> > +  * Otherwise we risk the next pipe updating before this
> > pipe
> > +  * finishes, resulting in the pipe fetching from ddb space
> > for
> > +  * the wrong pipe.
> > +  *
> > +  * However, if we know we don't have any more pipes to move
> > +  * around, we can skip this wait and the new ddb allocation
> > +  * will take effect at the start of the next vblank.
> > +  */
> > + switch (step) {
> > + case SKL_DDB_STEP_NO_OVERLAP:
> > + case SKL_DDB_STEP_OVERLAP:
> > + if (step != intel_state->last_ddb_step)
> > + vblank_wait = true;
> > +
> > + /* drop through */
> > + case SKL_DDB_STEP_FINAL:
> > + DRM_DEBUG_KMS(
> > +     "Updating [CRTC:%d:pipe %c] for DDB step %d\n",
> > +     crtc->base.id, pipe_name(intel_crtc->pipe),
> > +     step);
> > +
> > + case SKL_DDB_STEP_NONE:
> > + break;
> > + }
>
> Not sure we really need this step stuff. How about?
>
> for_each_crtc
> if (crtc_needs_disabling)
> disable_crtc();
>
> do {
> progress = false;
> wait_vbl_pipes=0;
> for_each_crtc() {
> if (!active || needs_modeset)
> continue;
> if (!ddb_changed)
> continue;
> if (new_ddb_overlaps_with_any_other_pipes_current_ddb)
> continue;
> commit;
> wait_vbl_pipes |= pipe;
> progress = true;
> }
> wait_vbls(wait_vbl_pipes);
> } while (progress);
>
> for_each_crtc
> if (crtc_needs_enabling)
> enable_crtc();
> commit;
> }

I'm fine with this, it might make this logic a little easier to read.
>
> Or if we're paranoid, we could also have an upper bound on the
> loop and assert that we never reach it.
>
>
> Though one thing I don't particularly like about this commit while
> changing the ddb approach is that it's going to make the update
> appear even less atomic. What I'd rather like to do for the normal
> commit path is this:
>
> for_each_crtc
> if (crtc_needs_disabling)
> disable_planes
> for_each_crtc
> if (crtc_needs_disabling)
> disable_crtc
> for_each_crtc
> if (crtc_needs_enabling)
> enable_crtc
> for_each_crtc
> if (active)
> commit_planes;
>
> That way everything would pop in and out as close together as possible.
> Hmm. Actually, I wonder... I'm thinking we should be able to enable all
> crtcs prior to entering the ddb commit loop, on account of no planes
> being enabled on those crtcs until we commit them. And if no planes are
> enabled, running the pipe w/o allocated ddb should be fine. So with that
> approach, I think we should be able to commit all planes within a few
> iterations of the loop, and hence within a few vblanks.

I can't see any issues with this, and this would definitely make the code a lot
cleaner. I'm alright with going this route if matt doesn't see any issues with
it as well.

Cheers,
Lyude

>
> >
> > +
> > + intel_update_crtc(crtc, state, old_crtc_state,
> > +   &crtc_vblank_mask);
> > +
> > + if (vblank_wait)
> > + intel_wait_for_vblank(state->dev, intel_crtc-
> > >pipe);
> > + }
> > +}
> > +
> > +static void skl_update_crtcs(struct drm_atomic_state *state,
> > +      unsigned int *crtc_vblank_mask)
> > +{
> > + struct intel_atomic_state *intel_state =
> > to_intel_atomic_state(state);
> > + enum skl_ddb_step step;
> > +
> > + for (step = 0; step <= intel_state->last_ddb_step; step++)
> > + skl_do_ddb_step(state, step);
> > +}
> > +
> >  static void intel_atomic_commit_tail(struct drm_atomic_state *state)
> >  {
> >   struct drm_device *dev = state->dev;
> > @@ -15235,8 +15308,6 @@ void intel_init_display_hooks(struct
> > drm_i915_private *dev_priv)
> >   dev_priv->display.crtc_disable = i9xx_crtc_disable;
> >   }
> >
> > - dev_priv->display.update_crtcs = intel_update_crtcs;
> > -
> >   /* Returns the core display clock speed */
> >   if (IS_SKYLAKE(dev_priv) || IS_KABYLAKE(dev_priv))
> >   dev_priv->display.get_display_clock_speed =
> > @@ -15326,6 +15397,11 @@ void intel_init_display_hooks(struct
> > drm_i915_private *dev_priv)
> >   skl_modeset_calc_cdclk;
> >   }
> >
> > + if (dev_priv->info.gen >= 9)
> > + dev_priv->display.update_crtcs = skl_update_crtcs;
> > + else
> > + dev_priv->display.update_crtcs = intel_update_crtcs;
> > +
> >   switch (INTEL_INFO(dev_priv)->gen) {
> >   case 2:
> >   dev_priv->display.queue_flip = intel_gen2_queue_flip;
> > diff --git a/drivers/gpu/drm/i915/intel_drv.h
> > b/drivers/gpu/drm/i915/intel_drv.h
> > index 1b444d3..cf5da83 100644
> > --- a/drivers/gpu/drm/i915/intel_drv.h
> > +++ b/drivers/gpu/drm/i915/intel_drv.h
> > @@ -334,6 +334,7 @@ struct intel_atomic_state {
> >
> >   /* Gen9+ only */
> >   struct skl_wm_values wm_results;
> > + int last_ddb_step;
> >  };
> >
> >  struct intel_plane_state {
> > @@ -437,6 +438,13 @@ struct skl_pipe_wm {
> >   uint32_t linetime;
> >  };
> >
> > +enum skl_ddb_step {
> > + SKL_DDB_STEP_NONE = 0,
> > + SKL_DDB_STEP_NO_OVERLAP,
> > + SKL_DDB_STEP_OVERLAP,
> > + SKL_DDB_STEP_FINAL
> > +};
> > +
> >  struct intel_crtc_wm_state {
> >   union {
> >   struct {
> > @@ -467,6 +475,8 @@ struct intel_crtc_wm_state {
> >   /* minimum block allocation */
> >   uint16_t minimum_blocks[I915_MAX_PLANES];
> >   uint16_t minimum_y_blocks[I915_MAX_PLANES];
> > +
> > + enum skl_ddb_step ddb_realloc;
> >   } skl;
> >   };
> >
> > diff --git a/drivers/gpu/drm/i915/intel_pm.c
> > b/drivers/gpu/drm/i915/intel_pm.c
> > index 6f5beb3..636c90a 100644
> > --- a/drivers/gpu/drm/i915/intel_pm.c
> > +++ b/drivers/gpu/drm/i915/intel_pm.c
> > @@ -3816,6 +3816,11 @@ void skl_write_plane_wm(struct intel_crtc
> > *intel_crtc,
> >      wm->plane[pipe][plane][level]);
> >   }
> >   I915_WRITE(PLANE_WM_TRANS(pipe, plane), wm-
> > >plane_trans[pipe][plane]);
> > +
> > + skl_ddb_entry_write(dev_priv, PLANE_BUF_CFG(pipe, plane),
> > +     &wm->ddb.plane[pipe][plane]);
> > + skl_ddb_entry_write(dev_priv, PLANE_NV12_BUF_CFG(pipe, plane),
> > +     &wm->ddb.y_plane[pipe][plane]);
> >  }
> >
> >  void skl_write_cursor_wm(struct intel_crtc *intel_crtc,
> > @@ -3832,170 +3837,51 @@ void skl_write_cursor_wm(struct intel_crtc
> > *intel_crtc,
> >      wm->plane[pipe][PLANE_CURSOR][level]);
> >   }
> >   I915_WRITE(CUR_WM_TRANS(pipe), wm-
> > >plane_trans[pipe][PLANE_CURSOR]);
> > -}
> > -
> > -static void skl_write_wm_values(struct drm_i915_private *dev_priv,
> > - const struct skl_wm_values *new)
> > -{
> > - struct drm_device *dev = &dev_priv->drm;
> > - struct intel_crtc *crtc;
> > -
> > - for_each_intel_crtc(dev, crtc) {
> > - int i;
> > - enum pipe pipe = crtc->pipe;
> > -
> > - if ((new->dirty_pipes & drm_crtc_mask(&crtc->base)) == 0)
> > - continue;
> > - if (!crtc->active)
> > - continue;
> >
> > - for (i = 0; i < intel_num_planes(crtc); i++) {
> > - skl_ddb_entry_write(dev_priv,
> > -     PLANE_BUF_CFG(pipe, i),
> > -     &new->ddb.plane[pipe][i]);
> > - skl_ddb_entry_write(dev_priv,
> > -     PLANE_NV12_BUF_CFG(pipe, i),
> > -     &new->ddb.y_plane[pipe][i]);
> > - }
> > -
> > - skl_ddb_entry_write(dev_priv, CUR_BUF_CFG(pipe),
> > -     &new->ddb.plane[pipe][PLANE_CURSOR]);
> > - }
> > + skl_ddb_entry_write(dev_priv, CUR_BUF_CFG(pipe),
> > +     &wm->ddb.plane[pipe][PLANE_CURSOR]);
> >  }
> >
> > -/*
> > - * When setting up a new DDB allocation arrangement, we need to correctly
> > - * sequence the times at which the new allocations for the pipes are taken
> > into
> > - * account or we'll have pipes fetching from space previously allocated to
> > - * another pipe.
> > - *
> > - * Roughly the sequence looks like:
> > - *  1. re-allocate the pipe(s) with the allocation being reduced and not
> > - *     overlapping with a previous light-up pipe (another way to put it is:
> > - *     pipes with their new allocation strickly included into their old
> > ones).
> > - *  2. re-allocate the other pipes that get their allocation reduced
> > - *  3. allocate the pipes having their allocation increased
> > - *
> > - * Steps 1. and 2. are here to take care of the following case:
> > - * - Initially DDB looks like this:
> > - *     |   B    |   C    |
> > - * - enable pipe A.
> > - * - pipe B has a reduced DDB allocation that overlaps with the old pipe C
> > - *   allocation
> > - *     |  A  |  B  |  C  |
> > - *
> > - * We need to sequence the re-allocation: C, B, A (and not B, C, A).
> > - */
> > -
> > -static void
> > -skl_wm_flush_pipe(struct drm_i915_private *dev_priv, enum pipe pipe, int
> > pass)
> > +static bool
> > +skl_ddb_allocation_equals(const struct skl_ddb_allocation *old,
> > +   const struct skl_ddb_allocation *new,
> > +   enum pipe pipe)
> >  {
> > - int plane;
> > -
> > - DRM_DEBUG_KMS("flush pipe %c (pass %d)\n", pipe_name(pipe), pass);
> > -
> > - for_each_plane(dev_priv, pipe, plane) {
> > - I915_WRITE(PLANE_SURF(pipe, plane),
> > -    I915_READ(PLANE_SURF(pipe, plane)));
> > - }
> > - I915_WRITE(CURBASE(pipe), I915_READ(CURBASE(pipe)));
> > + return new->pipe[pipe].start == old->pipe[pipe].start &&
> > +        new->pipe[pipe].end == old->pipe[pipe].end;
> >  }
> >
> >  static bool
> > -skl_ddb_allocation_included(const struct skl_ddb_allocation *old,
> > +skl_ddb_allocation_overlaps(struct drm_atomic_state *state,
> > +     const struct skl_ddb_allocation *old,
> >       const struct skl_ddb_allocation *new,
> >       enum pipe pipe)
> >  {
> > - uint16_t old_size, new_size;
> > -
> > - old_size = skl_ddb_entry_size(&old->pipe[pipe]);
> > - new_size = skl_ddb_entry_size(&new->pipe[pipe]);
> > -
> > - return old_size != new_size &&
> > -        new->pipe[pipe].start >= old->pipe[pipe].start &&
> > -        new->pipe[pipe].end <= old->pipe[pipe].end;
> > -}
> > -
> > -static void skl_flush_wm_values(struct drm_i915_private *dev_priv,
> > - struct skl_wm_values *new_values)
> > -{
> > - struct drm_device *dev = &dev_priv->drm;
> > - struct skl_ddb_allocation *cur_ddb, *new_ddb;
> > - bool reallocated[I915_MAX_PIPES] = {};
> > - struct intel_crtc *crtc;
> > - enum pipe pipe;
> > -
> > - new_ddb = &new_values->ddb;
> > - cur_ddb = &dev_priv->wm.skl_hw.ddb;
> > -
> > - /*
> > -  * First pass: flush the pipes with the new allocation contained
> > into
> > -  * the old space.
> > -  *
> > -  * We'll wait for the vblank on those pipes to ensure we can safely
> > -  * re-allocate the freed space without this pipe fetching from it.
> > -  */
> > - for_each_intel_crtc(dev, crtc) {
> > - if (!crtc->active)
> > - continue;
> > -
> > - pipe = crtc->pipe;
> > -
> > - if (!skl_ddb_allocation_included(cur_ddb, new_ddb, pipe))
> > - continue;
> > -
> > - skl_wm_flush_pipe(dev_priv, pipe, 1);
> > - intel_wait_for_vblank(dev, pipe);
> > -
> > - reallocated[pipe] = true;
> > - }
> > -
> > -
> > - /*
> > -  * Second pass: flush the pipes that are having their allocation
> > -  * reduced, but overlapping with a previous allocation.
> > -  *
> > -  * Here as well we need to wait for the vblank to make sure the
> > freed
> > -  * space is not used anymore.
> > -  */
> > - for_each_intel_crtc(dev, crtc) {
> > - if (!crtc->active)
> > - continue;
> > -
> > - pipe = crtc->pipe;
> > -
> > - if (reallocated[pipe])
> > - continue;
> > -
> > - if (skl_ddb_entry_size(&new_ddb->pipe[pipe]) <
> > -     skl_ddb_entry_size(&cur_ddb->pipe[pipe])) {
> > - skl_wm_flush_pipe(dev_priv, pipe, 2);
> > - intel_wait_for_vblank(dev, pipe);
> > - reallocated[pipe] = true;
> > - }
> > - }
> > -
> > - /*
> > -  * Third pass: flush the pipes that got more space allocated.
> > -  *
> > -  * We don't need to actively wait for the update here, next vblank
> > -  * will just get more DDB space with the correct WM values.
> > -  */
> > - for_each_intel_crtc(dev, crtc) {
> > - if (!crtc->active)
> > - continue;
> > + struct drm_device *dev = state->dev;
> > + struct intel_crtc *intel_crtc;
> > + enum pipe otherp;
> >
> > - pipe = crtc->pipe;
> > + for_each_intel_crtc(dev, intel_crtc) {
> > + otherp = intel_crtc->pipe;
> >
> >   /*
> > -  * At this point, only the pipes more space than before are
> > -  * left to re-allocate.
> > +  * When checking for overlaps, we don't want to:
> > +  *  - Compare against ourselves
> > +  *  - Compare against pipes that will be disabled in step 0
> > +  *  - Compare against pipes that won't be enabled until
> > step 3
> >    */
> > - if (reallocated[pipe])
> > + if (otherp == pipe || !new->pipe[otherp].end ||
> > +     !old->pipe[otherp].end)
> >   continue;
> >
> > - skl_wm_flush_pipe(dev_priv, pipe, 3);
> > + if ((new->pipe[pipe].start >= old->pipe[otherp].start &&
> > +      new->pipe[pipe].start < old->pipe[otherp].end) ||
> > +     (old->pipe[otherp].start >= new->pipe[pipe].start &&
> > +      old->pipe[otherp].start < new->pipe[pipe].end))
> > + return true;
> >   }
> > +
> > + return false;
> >  }
> >
> >  static int skl_update_pipe_wm(struct drm_crtc_state *cstate,
> > @@ -4038,8 +3924,10 @@ skl_compute_ddb(struct drm_atomic_state *state)
> >   struct drm_device *dev = state->dev;
> >   struct drm_i915_private *dev_priv = to_i915(dev);
> >   struct intel_atomic_state *intel_state =
> > to_intel_atomic_state(state);
> > + struct intel_crtc_state *cstate;
> >   struct intel_crtc *intel_crtc;
> > - struct skl_ddb_allocation *ddb = &intel_state->wm_results.ddb;
> > + struct skl_ddb_allocation *old_ddb = &dev_priv->wm.skl_hw.ddb;
> > + struct skl_ddb_allocation *new_ddb = &intel_state->wm_results.ddb;
> >   uint32_t realloc_pipes = pipes_modified(state);
> >   int ret;
> >
> > @@ -4071,13 +3959,11 @@ skl_compute_ddb(struct drm_atomic_state *state)
> >   }
> >
> >   for_each_intel_crtc_mask(dev, intel_crtc, realloc_pipes) {
> > - struct intel_crtc_state *cstate;
> > -
> >   cstate = intel_atomic_get_crtc_state(state, intel_crtc);
> >   if (IS_ERR(cstate))
> >   return PTR_ERR(cstate);
> >
> > - ret = skl_allocate_pipe_ddb(cstate, ddb);
> > + ret = skl_allocate_pipe_ddb(cstate, new_ddb);
> >   if (ret)
> >   return ret;
> >
> > @@ -4086,6 +3972,73 @@ skl_compute_ddb(struct drm_atomic_state *state)
> >   return ret;
> >   }
> >
> > + /*
> > +  * When setting up a new DDB allocation arrangement, we need to
> > +  * correctly sequence the times at which the new allocations for
> > the
> > +  * pipes are taken into account or we'll have pipes fetching from
> > space
> > +  * previously allocated to another pipe.
> > +  *
> > +  * Roughly the final sequence we want looks like this:
> > +  *  1. Disable any pipes we're not going to be using anymore
> > +  *  2. Reallocate all of the active pipes whose new ddb allocations
> > +  *  won't overlap with another active pipe's ddb allocation.
> > +  *  3. Reallocate remaining active pipes, if any.
> > +  *  4. Enable any new pipes, if any.
> > +  *
> > +  * Example:
> > +  * Initially DDB looks like this:
> > +  *   |   B    |   C    |
> > +  * And the final DDB should look like this:
> > +  *   |  B  |  C  |  A  |
> > +  *
> > +  * 1. We're not disabling any pipes, so do nothing on this step.
> > +  * 2. Pipe B's new allocation wouldn't overlap with pipe C, however
> > +  * pipe C's new allocation does overlap with pipe B's current
> > +  * allocation. Reallocate B first so the DDB looks like this:
> > +  *   |  B  |xx|   C    |
> > +  * 3. Now we can safely reallocate pipe C to it's new location:
> > +  *   |  B  |  C  |xxxxx|
> > +  * 4. Enable any remaining pipes, in this case A
> > +  *   |  B  |  C  |  A  |
> > +  *
> > +  * As well, between every pipe reallocation we have to wait for a
> > +  * vblank on the pipe so that we ensure it's new allocation has
> > taken
> > +  * effect by the time we start moving the next pipe. This can be
> > +  * skipped on the last step we need to perform, which is why we
> > keep
> > +  * track of that information here. For example, if we've
> > reallocated
> > +  * all the pipes that need changing by the time we reach step 3, we
> > can
> > +  * finish without waiting for the pipes we changed in step 3 to
> > update.
> > +  */
> > + for_each_intel_crtc_mask(dev, intel_crtc, realloc_pipes) {
> > + enum pipe pipe = intel_crtc->pipe;
> > + enum skl_ddb_step step;
> > +
> > + cstate = intel_atomic_get_crtc_state(state, intel_crtc);
> > + if (IS_ERR(cstate))
> > + return PTR_ERR(cstate);
> > +
> > + /* Step 1: Pipes we're disabling / haven't changed */
> > + if (skl_ddb_allocation_equals(old_ddb, new_ddb, pipe) ||
> > +     new_ddb->pipe[pipe].end == 0) {
> > + step = SKL_DDB_STEP_NONE;
> > + /* Step 2-3: Active pipes we're reallocating */
> > + } else if (old_ddb->pipe[pipe].end != 0) {
> > + if (skl_ddb_allocation_overlaps(state, old_ddb,
> > new_ddb,
> > + pipe))
> > + step = SKL_DDB_STEP_OVERLAP;
> > + else
> > + step = SKL_DDB_STEP_NO_OVERLAP;
> > + /* Step 4: Pipes we're enabling */
> > + } else {
> > + step = SKL_DDB_STEP_FINAL;
> > + }
> > +
> > + cstate->wm.skl.ddb_realloc = step;
> > +
> > + if (step > intel_state->last_ddb_step)
> > + intel_state->last_ddb_step = step;
> > + }
> > +
> >   return 0;
> >  }
> >
> > @@ -4110,10 +4063,13 @@ skl_copy_wm_for_pipe(struct skl_wm_values *dst,
> >  static int
> >  skl_compute_wm(struct drm_atomic_state *state)
> >  {
> > + struct drm_i915_private *dev_priv = to_i915(state->dev);
> >   struct drm_crtc *crtc;
> >   struct drm_crtc_state *cstate;
> >   struct intel_atomic_state *intel_state =
> > to_intel_atomic_state(state);
> >   struct skl_wm_values *results = &intel_state->wm_results;
> > + struct skl_ddb_allocation *old_ddb = &dev_priv->wm.skl_hw.ddb;
> > + struct skl_ddb_allocation *new_ddb = &results->ddb;
> >   struct skl_pipe_wm *pipe_wm;
> >   bool changed = false;
> >   int ret, i;
> > @@ -4152,7 +4108,10 @@ skl_compute_wm(struct drm_atomic_state *state)
> >   struct intel_crtc *intel_crtc = to_intel_crtc(crtc);
> >   struct intel_crtc_state *intel_cstate =
> >   to_intel_crtc_state(cstate);
> > + enum skl_ddb_step step;
> > + enum pipe pipe;
> >
> > + pipe = intel_crtc->pipe;
> >   pipe_wm = &intel_cstate->wm.skl.optimal;
> >   ret = skl_update_pipe_wm(cstate, &results->ddb, pipe_wm,
> >    &changed);
> > @@ -4167,7 +4126,18 @@ skl_compute_wm(struct drm_atomic_state *state)
> >   continue;
> >
> >   intel_cstate->update_wm_pre = true;
> > + step = intel_cstate->wm.skl.ddb_realloc;
> >   skl_compute_wm_results(crtc->dev, pipe_wm, results,
> > intel_crtc);
> > +
> > + if (!skl_ddb_entry_equal(&old_ddb->pipe[pipe],
> > +  &new_ddb->pipe[pipe])) {
> > + DRM_DEBUG_KMS(
> > +     "DDB changes for [CRTC:%d:pipe %c]: (%3d - %3d)
> > -> (%3d - %3d) on step %d\n",
> > +     intel_crtc->base.base.id, pipe_name(pipe),
> > +     old_ddb->pipe[pipe].start, old_ddb-
> > >pipe[pipe].end,
> > +     new_ddb->pipe[pipe].start, new_ddb-
> > >pipe[pipe].end,
> > +     step);
> > + }
> >   }
> >
> >   return 0;
> > @@ -4191,8 +4161,20 @@ static void skl_update_wm(struct drm_crtc *crtc)
> >
> >   mutex_lock(&dev_priv->wm.wm_mutex);
> >
> > - skl_write_wm_values(dev_priv, results);
> > - skl_flush_wm_values(dev_priv, results);
> > + /*
> > +  * If this pipe isn't active already, we're going to be enabling it
> > +  * very soon. Since it's safe to update these while the pipe's shut
> > off,
> > +  * just do so here. Already active pipes will have their watermarks
> > +  * updated once we update their planes.
> > +  */
> > + if (!intel_crtc->active) {
> > + int plane;
> > +
> > + for (plane = 0; plane < intel_num_planes(intel_crtc);
> > plane++)
> > + skl_write_plane_wm(intel_crtc, results, plane);
> > +
> > + skl_write_cursor_wm(intel_crtc, results);
> > + }
> >
> >   /*
> >    * Store the new configuration (but only for the pipes that have
> > --
> > 2.7.4
>
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