Since this patch has been on hold for a little bit, I did a bit of
thinking of how we could this a little more cleanly. Unfortunately I
couldn't think of a way, however I did think of an alternative
solution:
I'm planning on backporting all of the skl wm fixes already, so I'm
going to use this patch for that since it's very small. As for
mainline, I'm going to do a whole reorganization of the skl wm/ddb
structs in i915 like Matt had suggested before. Things might look a
little more like this (taken from my half-complete reorganization):
struct skl_plane_ddb_allocation {
struct skl_ddb_entry plane;
struct skl_ddb_entry y_plane;
};
struct skl_plane_wm_values {
struct skl_plane_ddb_allocation ddb;
uint32_t wm[8];
uint32_t trans_wm;
};
struct skl_pipe_wm_values {
struct skl_ddb_entry ddb;
uint32_t linetime;
};
struct skl_hw_wm_values { /* (only used for skl_get_hw_ddb and friends) */
struct skl_pipe_wm_values pipe[I915_MAX_PIPES];
struct skl_plane_wm_values plane[I915_MAX_PIPES][I915_MAX_PLANES];
};
As well, I'm also just going to completely remove the skl_results and
skl_hw structs from struct drm_i915_private. This makes sense for a lot
of reasons:
* This completely gets rid of the need for a global watermark lock (on
Skylake at least) and will make things a lot easier for atomic
support in the future
* Skylake doesn't have any actual global watermark hooks anyway, aside
from skl_update_wm() which is now only used for writing watermarks
for inactive pipes during haswell_crtc_enable()
* This makes passing watermarks around way less of a mess
* Saves a tiny bit of data, and so far being able to grab
watermarks/ddbs right from the plane states seems to be a lot easier
then messing with a large array
As for this fix, I'll probably still need someone to review it so I can
get it into 4.7.y.
Let me know what you think.
On Mon, 2016-08-29 at 12:31 -0400, Lyude wrote:
> i915 sometimes needs to disable planes in the middle of an atomic
> commit, and then reenable them later in the same commit. Because of
> this, we can't make the assumption that the state of the plane
> actually
> changed. Since the state of the plane hasn't actually changed,
> neither
> have it's watermarks. And if the watermarks hasn't changed then we
> haven't populated skl_results with anything, which means we'll end up
> zeroing out a plane's watermarks in the middle of the atomic commit
> without restoring them later.
>
> Simple reproduction recipe:
> - Get a SKL laptop, launch any kind of X session
> - Get two extra monitors
> - Keep hotplugging both displays (so that the display configuration
> jumps from 1 active pipe to 3 active pipes and back)
> - Eventually underrun
>
> Changes since v1:
> - Fix incorrect use of "it's"
> Changes since v2:
> - Add reproduction recipe
>
> Signed-off-by: Lyude <cpaul@xxxxxxxxxx>
> Cc: Maarten Lankhorst <maarten.lankhorst@xxxxxxxxxxxxxxx>
> Fixes: 62e0fb880123 ("drm/i915/skl: Update plane watermarks
> atomically
> during plane updates")
>
> Signed-off-by: Lyude <cpaul@xxxxxxxxxx>
> ---
> drivers/gpu/drm/i915/intel_display.c | 7 ++++++-
> drivers/gpu/drm/i915/intel_sprite.c | 9 +++++++--
> 2 files changed, 13 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/intel_display.c
> b/drivers/gpu/drm/i915/intel_display.c
> index e4e6141..13e47a7 100644
> --- a/drivers/gpu/drm/i915/intel_display.c
> +++ b/drivers/gpu/drm/i915/intel_display.c
> @@ -3448,7 +3448,12 @@ static void
> skylake_disable_primary_plane(struct drm_plane *primary,
> struct intel_crtc *intel_crtc = to_intel_crtc(crtc);
> int pipe = intel_crtc->pipe;
>
> - skl_write_plane_wm(intel_crtc, &dev_priv->wm.skl_results,
> 0);
> + /*
> + * We only populate skl_results on watermark updates, and if
> the
> + * plane's visiblity isn't actually changing neither is its
> watermarks.
> + */
> + if (!crtc->primary->state->visible)
> + skl_write_plane_wm(intel_crtc, &dev_priv-
> >wm.skl_results, 0);
>
> I915_WRITE(PLANE_CTL(pipe, 0), 0);
> I915_WRITE(PLANE_SURF(pipe, 0), 0);
> diff --git a/drivers/gpu/drm/i915/intel_sprite.c
> b/drivers/gpu/drm/i915/intel_sprite.c
> index 0df783a..73a521f 100644
> --- a/drivers/gpu/drm/i915/intel_sprite.c
> +++ b/drivers/gpu/drm/i915/intel_sprite.c
> @@ -292,8 +292,13 @@ skl_disable_plane(struct drm_plane *dplane,
> struct drm_crtc *crtc)
> const int pipe = intel_plane->pipe;
> const int plane = intel_plane->plane + 1;
>
> - skl_write_plane_wm(to_intel_crtc(crtc), &dev_priv-
> >wm.skl_results,
> - plane);
> + /*
> + * We only populate skl_results on watermark updates, and if
> the
> + * plane's visiblity isn't actually changing neither is its
> watermarks.
> + */
> + if (!dplane->state->visible)
> + skl_write_plane_wm(to_intel_crtc(crtc),
> + &dev_priv->wm.skl_results,
> plane);
>
> I915_WRITE(PLANE_CTL(pipe, plane), 0);
>
--
Cheers,
Lyude
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