Re: [PATCH v4 5/6] drm/i915/skl: Update plane watermarks atomically during plane updates

Matt Roper
2016-07-28T13:15:11Z

On Tue, Jul 26, 2016 at 01:34:41PM -0400, Lyude wrote:
> 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
>
> Fixes: 2d41c0b59afc ("drm/i915/skl: SKL Watermark Computation")
> Signed-off-by: Lyude <cpaul@redhat.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>
> Cc: Matt Roper <matthew.d.roper@intel.com>
> ---
> drivers/gpu/drm/i915/intel_display.c | 5 ++++
> drivers/gpu/drm/i915/intel_drv.h | 2 ++
> drivers/gpu/drm/i915/intel_pm.c | 58 ++++++++++++++++++++++++++----------
> drivers/gpu/drm/i915/intel_sprite.c | 2 ++
> 4 files changed, 51 insertions(+), 16 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
> index b80c051..cd67945 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);
> @@ -10261,6 +10263,9 @@ static void i9xx_update_cursor(struct drm_crtc *crtc, u32 base,
> int pipe = intel_crtc->pipe;
> uint32_t cntl = 0;
>
> + if (IS_GEN9(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 113bf48..e212ed9 100644
> --- a/drivers/gpu/drm/i915/intel_drv.h
> +++ b/drivers/gpu/drm/i915/intel_drv.h
> @@ -1711,6 +1711,8 @@ void skl_ddb_get_hw_state(struct drm_i915_private *dev_priv,
> struct skl_ddb_allocation *ddb /* out */);
> int skl_enable_sagv(struct drm_i915_private *dev_priv);
> int skl_disable_sagv(struct drm_i915_private *dev_priv);
> +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 fb5d2eb..d469ad2 100644
> --- a/drivers/gpu/drm/i915/intel_pm.c
> +++ b/drivers/gpu/drm/i915/intel_pm.c
> @@ -3783,6 +3783,47 @@ 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;
> +
> + if (!(wm->dirty_pipes & drm_crtc_mask(crtc)))
> + return;
> +
> + I915_WRITE(PIPE_WM_LINETIME(pipe), wm->wm_linetime[pipe]);

Putting this here may lead to it being programmed multiple times or not
at all, depending on what pipes are in use. Worst case is you have the
CRTC on with no planes except the cursor (and possibly the canvas), but
do a modeset or pipe scaling change that needs to change the linetime
watermark.

I guess we probably need a new device-specific callback from
intel_update_pipe_config() (which gets called by
intel_begin_crtc_commit()) where we can do this once per CRTC.

Matt

> +
> + 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;
> +
> + if (!(wm->dirty_pipes & drm_crtc_mask(crtc)))
> + return;
> +
> + 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)
> {
> @@ -3790,7 +3831,7 @@ static void skl_write_wm_values(struct drm_i915_private *dev_priv,
> struct intel_crtc *crtc;
>
> 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)
> @@ -3798,21 +3839,6 @@ static void skl_write_wm_values(struct drm_i915_private *dev_priv,
> if (!crtc->active)
> continue;
>
> - 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
>

--
Matt Roper
Graphics Software Engineer
IoTG Platform Enabling & Development
Intel Corporation
(916) 356-2795