Re: [PATCH v2 4/4] drm/i915/skl: Update plane watermarks atomically during plane updates

From: Matt Roper
Date: Thu Jul 21 2016 - 16:57:26 EST

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On Thu, Jul 21, 2016 at 03:23:40PM -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
>
> Fixes: 2d41c0b59afc ("drm/i915/skl: SKL Watermark Computation")
> Signed-off-by: Lyude <cpaul@xxxxxxxxxx>
> Cc: stable@xxxxxxxxxxxxxxx
> Cc: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx>
> Cc: Daniel Vetter <daniel.vetter@xxxxxxxxx>
> Cc: Radhakrishna Sripada <radhakrishna.sripada@xxxxxxxxx>
> Cc: Hans de Goede <hdegoede@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 | 54 ++++++++++++++++++++++++++----------
> drivers/gpu/drm/i915/intel_sprite.c | 2 ++
> 4 files changed, 49 insertions(+), 14 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
> index 78beb7e..d93d014 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_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 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 9421d92..41f379b 100644
> --- a/drivers/gpu/drm/i915/intel_pm.c
> +++ b/drivers/gpu/drm/i915/intel_pm.c
> @@ -3680,6 +3680,45 @@ 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;
> +
> + 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]);

I think we might as well write the DDB changes in this function too.
The DDB and WM's really need to be written in the same vblank, and our
three-step pipe flushing isn't really doing the right thing yet anyway.

After that we'd just need a final patch #5 of this series to change our
pipe iteration order (and include the necessary pipe vblank waits).

> +}
> +
> +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)
> {
> @@ -3687,7 +3726,7 @@ 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)
> @@ -3697,19 +3736,6 @@ static void skl_write_wm_values(struct drm_i915_private *dev_priv,
>
> I915_WRITE(PIPE_WM_LINETIME(pipe), new->wm_linetime[pipe]);

This probably needs to be moved under vblank evasion as well, otherwise
it can get updated vblank(s) earlier than the rest of the registers are
updated.

Matt

>
> - 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

Next message: Andrey Vagin: "[PATCH] namespace.7: descirbe NS_GET_USERNS and NS_GET-PARENT ioctl-s"
Previous message: Hoan Tran: "[PATCH v3 1/3] Documentation: dtb: xgene: Add hwmon dts binding documentation"
In reply to: Lyude: "[PATCH v2 4/4] drm/i915/skl: Update plane watermarks atomically during plane updates"
Next in thread: Lyude: "[PATCH v2 3/4] drm/i915/skl: Fix extra whitespace in skl_flush_wm_values()"
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