drm/i915/skl: Update plane watermarks atomically during plane updates
Thanks to Ville for suggesting this as a potential solution to pipe
underruns on Skylake.
On Skylake all of the registers for configuring planes, including the
registers for configuring their watermarks, are double buffered. New
values written to them won't take effect until said registers are
"armed", which is done by writing to the PLANE_SURF (or in the case of
cursor planes, the CURBASE register) register.
With this in mind, up until now we've been updating watermarks on skl
like this:
non-modeset {
- calculate (during atomic check phase)
- finish_atomic_commit:
- intel_pre_plane_update:
- intel_update_watermarks()
- {vblank happens; new watermarks + old plane values => underrun }
- drm_atomic_helper_commit_planes_on_crtc:
- start vblank evasion
- write new plane registers
- end vblank evasion
}
or
modeset {
- calculate (during atomic check phase)
- finish_atomic_commit:
- crtc_enable:
- intel_update_watermarks()
- {vblank happens; new watermarks + old plane values => underrun }
- drm_atomic_helper_commit_planes_on_crtc:
- start vblank evasion
- write new plane registers
- end vblank evasion
}
Now we update watermarks atomically like this:
non-modeset {
- calculate (during atomic check phase)
- finish_atomic_commit:
- intel_pre_plane_update:
- intel_update_watermarks() (wm values aren't written yet)
- drm_atomic_helper_commit_planes_on_crtc:
- start vblank evasion
- write new plane registers
- write new wm values
- end vblank evasion
}
modeset {
- calculate (during atomic check phase)
- finish_atomic_commit:
- crtc_enable:
- intel_update_watermarks() (actual wm values aren't written
yet)
- drm_atomic_helper_commit_planes_on_crtc:
- start vblank evasion
- write new plane registers
- write new wm values
- end vblank evasion
}
So this patch moves all of the watermark writes into the right place;
inside of the vblank evasion where we update all of the registers for
each plane. While this patch doesn't fix everything, it does allow us to
update the watermark values in the way the hardware expects us to.
Changes since original patch series:
- Remove mutex_lock/mutex_unlock since they don't do anything and we're
not touching global state
- Move skl_write_cursor_wm/skl_write_plane_wm functions into
intel_pm.c, make externally visible
- Add skl_write_plane_wm calls to skl_update_plane
- Fix conditional for for loop in skl_write_plane_wm (level < max_level
should be level <= max_level)
- Make diagram in commit more accurate to what's actually happening
- Add Fixes:
Changes since v1:
- Use IS_GEN9() instead of IS_SKYLAKE() since these fixes apply to more
then just Skylake
- Update description to make it clear this patch doesn't fix everything
- Check if pipes were actually changed before writing watermarks
Changes since v2:
- Write PIPE_WM_LINETIME during vblank evasion
Changes since v3:
- Rebase against new SAGV patch changes
Changes since v4:
- Add a parameter to choose what skl_wm_values struct to use when
writing new plane watermarks
Changes since v5:
- Remove cursor ddb entry write in skl_write_cursor_wm(), defer until
patch 6
- Write WM_LINETIME in intel_begin_crtc_commit()
Changes since v6:
- Remove redundant dirty_pipes check in skl_write_plane_wm (we check
this in all places where we call this function, and it was supposed
to have been removed earlier anyway)
- In i9xx_update_cursor(), use dev_priv->info.gen >= 9 instead of
IS_GEN9(dev_priv). We do this everywhere else and I'd imagine this
needs to be done for gen10 as well
Changes since v7:
- Fix rebase fail (unused variable obj)
- Make struct skl_wm_values *wm const
- Fix indenting
- Use INTEL_GEN() instead of dev_priv->info.gen
Changes since v8:
- Don't forget calls to skl_write_plane_wm() when disabling planes
- Use INTEL_GEN(), not INTEL_INFO()->gen in intel_begin_crtc_commit()
Fixes: 2d41c0b5 ("drm/i915/skl: SKL Watermark Computation")
Signed-off-by: 
Lyude <cpaul@redhat.com>
Reviewed-by: 
Matt Roper <matthew.d.roper@intel.com>
Cc: stable@vger.kernel.org
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>
Signed-off-by: 
Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1471884608-10671-1-git-send-email-cpaul@redhat.com
Link: http://patchwork.freedesktop.org/patch/msgid/1471884608-10671-1-git-send-email-cpaul@redhat.com
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