[PATCH v2 1/2] drm/i915/skl: Update plane watermarks atomically during plane updates

From: Lyude
Date: Tue Jul 19 2016 - 15:16:22 EST

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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
}

Which is more of a step in the right direction to fixing all of the
underrun issues we're currently seeing with skl

Changes since v1:
- 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

Signed-off-by: Lyude Paul <cpaul@xxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Cc: Ville SyrjÃlÃ <ville.syrjala@xxxxxxxxxxxxxxx>
Cc: Daniel Vetter <daniel.vetter@xxxxxxxxx>
Cc: Radhakrishna Sripada <radhakrishna.sripada@xxxxxxxxx>
Cc: Hans de Goede <hdegoede@xxxxxxxxxx> <cpaul@xxxxxxxxxx>
Cc: Matt Roper <matthew.d.roper@xxxxxxxxx>
---
drivers/gpu/drm/i915/intel_display.c | 5 ++++
drivers/gpu/drm/i915/intel_drv.h | 2 ++
drivers/gpu/drm/i915/intel_pm.c | 48 +++++++++++++++++++++++++-----------
drivers/gpu/drm/i915/intel_sprite.c | 2 ++
4 files changed, 43 insertions(+), 14 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index fb7d8fc5..1481b2b 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -3031,6 +3031,8 @@ static void skylake_update_primary_plane(struct drm_plane *plane,
intel_crtc->adjusted_x = x_offset;
intel_crtc->adjusted_y = y_offset;

+ skl_write_plane_wm(intel_crtc, 0);
+
I915_WRITE(PLANE_CTL(pipe, 0), plane_ctl);
I915_WRITE(PLANE_OFFSET(pipe, 0), plane_offset);
I915_WRITE(PLANE_SIZE(pipe, 0), plane_size);
@@ -10242,6 +10244,9 @@ static void i9xx_update_cursor(struct drm_crtc *crtc, u32 base,
int pipe = intel_crtc->pipe;
uint32_t cntl = 0;

+ if (IS_SKYLAKE(dev_priv))
+ skl_write_cursor_wm(intel_crtc);
+
if (plane_state && plane_state->visible) {
cntl = MCURSOR_GAMMA_ENABLE;
switch (plane_state->base.crtc_w) {
diff --git a/drivers/gpu/drm/i915/intel_drv.h b/drivers/gpu/drm/i915/intel_drv.h
index e74d851..f1f54d9 100644
--- a/drivers/gpu/drm/i915/intel_drv.h
+++ b/drivers/gpu/drm/i915/intel_drv.h
@@ -1709,6 +1709,8 @@ void ilk_wm_get_hw_state(struct drm_device *dev);
void skl_wm_get_hw_state(struct drm_device *dev);
void skl_ddb_get_hw_state(struct drm_i915_private *dev_priv,
struct skl_ddb_allocation *ddb /* out */);
+void skl_write_cursor_wm(struct intel_crtc *intel_crtc);
+void skl_write_plane_wm(struct intel_crtc *intel_crtc, int plane);
uint32_t ilk_pipe_pixel_rate(const struct intel_crtc_state *pipe_config);
bool ilk_disable_lp_wm(struct drm_device *dev);
int sanitize_rc6_option(struct drm_i915_private *dev_priv, int enable_rc6);
diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
index 213ad35..90c788d 100644
--- a/drivers/gpu/drm/i915/intel_pm.c
+++ b/drivers/gpu/drm/i915/intel_pm.c
@@ -3776,6 +3776,39 @@ static void skl_ddb_entry_write(struct drm_i915_private *dev_priv,
I915_WRITE(reg, 0);
}

+void skl_write_plane_wm(struct intel_crtc *intel_crtc,
+ int plane)
+{
+ struct drm_crtc *crtc = &intel_crtc->base;
+ struct drm_device *dev = crtc->dev;
+ struct drm_i915_private *dev_priv = to_i915(dev);
+ struct skl_wm_values *wm = &dev_priv->wm.skl_results;
+ int level, max_level = ilk_wm_max_level(dev);
+ enum pipe pipe = intel_crtc->pipe;
+
+ for (level = 0; level <= max_level; level++) {
+ I915_WRITE(PLANE_WM(pipe, plane, level),
+ wm->plane[pipe][plane][level]);
+ }
+ I915_WRITE(PLANE_WM_TRANS(pipe, plane), wm->plane_trans[pipe][plane]);
+}
+
+void skl_write_cursor_wm(struct intel_crtc *intel_crtc)
+{
+ struct drm_crtc *crtc = &intel_crtc->base;
+ struct drm_device *dev = crtc->dev;
+ struct drm_i915_private *dev_priv = to_i915(dev);
+ struct skl_wm_values *wm = &dev_priv->wm.skl_results;
+ int level, max_level = ilk_wm_max_level(dev);
+ enum pipe pipe = intel_crtc->pipe;
+
+ for (level = 0; level <= max_level; level++) {
+ I915_WRITE(CUR_WM(pipe, level),
+ 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)
{
@@ -3788,7 +3821,7 @@ static void skl_write_wm_values(struct drm_i915_private *dev_priv,
skl_disable_sagv(dev_priv);

for_each_intel_crtc(dev, crtc) {
- int i, level, max_level = ilk_wm_max_level(dev);
+ int i;
enum pipe pipe = crtc->pipe;

if ((new->dirty_pipes & drm_crtc_mask(&crtc->base)) == 0)
@@ -3798,19 +3831,6 @@ static void skl_write_wm_values(struct drm_i915_private *dev_priv,

I915_WRITE(PIPE_WM_LINETIME(pipe), new->wm_linetime[pipe]);

- for (level = 0; level <= max_level; level++) {
- for (i = 0; i < intel_num_planes(crtc); i++)
- I915_WRITE(PLANE_WM(pipe, i, level),
- new->plane[pipe][i][level]);
- I915_WRITE(CUR_WM(pipe, level),
- new->plane[pipe][PLANE_CURSOR][level]);
- }
- for (i = 0; i < intel_num_planes(crtc); i++)
- I915_WRITE(PLANE_WM_TRANS(pipe, i),
- new->plane_trans[pipe][i]);
- I915_WRITE(CUR_WM_TRANS(pipe),
- new->plane_trans[pipe][PLANE_CURSOR]);
-
for (i = 0; i < intel_num_planes(crtc); i++) {
skl_ddb_entry_write(dev_priv,
PLANE_BUF_CFG(pipe, i),
diff --git a/drivers/gpu/drm/i915/intel_sprite.c b/drivers/gpu/drm/i915/intel_sprite.c
index 0de935a..50026f1 100644
--- a/drivers/gpu/drm/i915/intel_sprite.c
+++ b/drivers/gpu/drm/i915/intel_sprite.c
@@ -238,6 +238,8 @@ skl_update_plane(struct drm_plane *drm_plane,
crtc_w--;
crtc_h--;

+ skl_write_plane_wm(to_intel_crtc(crtc_state->base.crtc), plane);
+
if (key->flags) {
I915_WRITE(PLANE_KEYVAL(pipe, plane), key->min_value);
I915_WRITE(PLANE_KEYMAX(pipe, plane), key->max_value);
--
2.7.4

Next message: Tejun Heo: "Re: [PATCH v3 1/4] lib/dlock-list: Distributed and lock-protected lists"
Previous message: Kees Cook: "Re: [PATCH v3 02/11] mm: Hardened usercopy"
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