Re: [PATCH 3/4] drm/i915: Sanitize watermarks after hardware state readout (v2)

[Jani Nikula <jani.nikula@intel.com>]

On Tue, 03 Nov 2015, Matt Roper <matthew.d.roper@intel.com> wrote:
> Although we can do a good job of reading out hardware state, the
> graphics firmware may have programmed the watermarks in a creative way
> that doesn't match how i915 would have chosen to program them.  We
> shouldn't trust the firmware's watermark programming, but should rather
> re-calculate how we think WM's should be programmed and then shove those
> values into the hardware.
>
> We can do this pretty easily by creating a dummy top-level state,
> running it through the check process to calculate all the values, and
> then just programming the watermarks for each CRTC.
>
> v2:  Move watermark sanitization after our BIOS fb reconstruction; the
>      watermark calculations that we do here need to look at pstate->fb,
>      which isn't setup yet in intel_modeset_setup_hw_state(), even
>      though we have an enabled & visible plane.
>
> Cc: Jani Nikula <jani.nikula@intel.com>
> Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
> Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
> ---
> Jani, based on your logs it looks like the culprit is that we're calculating
> watermarks at startup time after we've read out preliminary hardware state (so
> we know the primary plane is enabled & visible), but before we reconstruct the
> BIOS fb (so pstate->fb is NULL).  I think moving the watermark sanitization
> later in the process so that we'll have a proper fb setup should hopefully
> solve the issue.  Can you test this version when you get a chance?  I'll also
> send a rebased patch #4 since the code movement here means that the previous
> version won't apply cleanly.

Sorry Matt, black screen with new versions of patches 3-4. Dmesg at
http://pastebin.com/3LXZwvWu

BR,
Jani.



>
>  drivers/gpu/drm/i915/i915_drv.h      |  1 +
>  drivers/gpu/drm/i915/intel_display.c | 55 ++++++++++++++++++++++++++++++++++++
>  drivers/gpu/drm/i915/intel_pm.c      | 14 +++++----
>  3 files changed, 64 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
> index 20cd6d8..09807c8 100644
> --- a/drivers/gpu/drm/i915/i915_drv.h
> +++ b/drivers/gpu/drm/i915/i915_drv.h
> @@ -629,6 +629,7 @@ struct drm_i915_display_funcs {
>  			  struct dpll *best_clock);
>  	int (*compute_pipe_wm)(struct intel_crtc *crtc,
>  			       struct drm_atomic_state *state);
> +	void (*program_watermarks)(struct intel_crtc_state *cstate);
>  	void (*update_wm)(struct drm_crtc *crtc);
>  	int (*modeset_calc_cdclk)(struct drm_atomic_state *state);
>  	void (*modeset_commit_cdclk)(struct drm_atomic_state *state);
> diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
> index 7b3cfb6..e289311 100644
> --- a/drivers/gpu/drm/i915/intel_display.c
> +++ b/drivers/gpu/drm/i915/intel_display.c
> @@ -14936,6 +14936,54 @@ void intel_modeset_init_hw(struct drm_device *dev)
>  	intel_enable_gt_powersave(dev);
>  }
>  
> +/*
> + * Calculate what we think the watermarks should be for the state we've read
> + * out of the hardware and then immediately program those watermarks so that
> + * we ensure the hardware settings match our internal state.
> + */
> +static void sanitize_watermarks(struct drm_device *dev)
> +{
> +	struct drm_i915_private *dev_priv = to_i915(dev);
> +	struct drm_atomic_state *state;
> +	struct drm_crtc *crtc;
> +	struct drm_crtc_state *cstate;
> +	int ret;
> +	int i;
> +
> +	/* Only supported on platforms that use atomic watermark design */
> +	if (!dev_priv->display.program_watermarks)
> +		return;
> +
> +	/*
> +	 * Calculate what we think WM's should be by creating a dummy state and
> +	 * running it through the atomic check code.
> +	 */
> +	state = drm_atomic_helper_duplicate_state(dev,
> +						  dev->mode_config.acquire_ctx);
> +	if (WARN_ON(IS_ERR(state)))
> +		return;
> +
> +	ret = intel_atomic_check(dev, state);
> +	if (ret) {
> +		/*
> +		 * Just give up and leave watermarks untouched if we get an
> +		 * error back from 'check'
> +		 */
> +		DRM_DEBUG_KMS("Could not determine valid watermarks for inherited state\n");
> +		return;
> +	}
> +
> +	/* Write calculated watermark values back */
> +	to_i915(dev)->wm.config = to_intel_atomic_state(state)->wm_config;
> +	for_each_crtc_in_state(state, crtc, cstate, i) {
> +		struct intel_crtc_state *cs = to_intel_crtc_state(cstate);
> +
> +		dev_priv->display.program_watermarks(cs);
> +	}
> +
> +	drm_atomic_state_free(state);
> +}
> +
>  void intel_modeset_init(struct drm_device *dev)
>  {
>  	struct drm_i915_private *dev_priv = dev->dev_private;
> @@ -15059,6 +15107,13 @@ void intel_modeset_init(struct drm_device *dev)
>  		 */
>  		intel_find_initial_plane_obj(crtc, &plane_config);
>  	}
> +
> +	/*
> +	 * Make sure hardware watermarks really match the state we read out.
> +	 * Note that we need to do this after reconstructing the BIOS fb's
> +	 * since the watermark calculation done here will use pstate->fb.
> +	 */
> +	sanitize_watermarks(dev);
>  }
>  
>  static void intel_enable_pipe_a(struct drm_device *dev)
> diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
> index 180348b..fbcb072 100644
> --- a/drivers/gpu/drm/i915/intel_pm.c
> +++ b/drivers/gpu/drm/i915/intel_pm.c
> @@ -3611,15 +3611,19 @@ static void skl_update_wm(struct drm_crtc *crtc)
>  	dev_priv->wm.skl_hw = *results;
>  }
>  
> -static void ilk_program_watermarks(struct drm_i915_private *dev_priv)
> +static void ilk_program_watermarks(struct intel_crtc_state *cstate)
>  {
> -	struct drm_device *dev = dev_priv->dev;
> +	struct drm_crtc *crtc = cstate->base.crtc;
> +	struct drm_device *dev = crtc->dev;
> +	struct drm_i915_private *dev_priv = to_i915(dev);
>  	struct intel_pipe_wm lp_wm_1_2 = {}, lp_wm_5_6 = {}, *best_lp_wm;
>  	struct ilk_wm_maximums max;
>  	struct intel_wm_config *config = &dev_priv->wm.config;
>  	struct ilk_wm_values results = {};
>  	enum intel_ddb_partitioning partitioning;
>  
> +	to_intel_crtc(crtc)->wm.active.ilk = cstate->wm.optimal.ilk;
> +
>  	ilk_compute_wm_maximums(dev, 1, config, INTEL_DDB_PART_1_2, &max);
>  	ilk_wm_merge(dev, config, &max, &lp_wm_1_2);
>  
> @@ -3644,7 +3648,6 @@ static void ilk_program_watermarks(struct drm_i915_private *dev_priv)
>  
>  static void ilk_update_wm(struct drm_crtc *crtc)
>  {
> -	struct drm_i915_private *dev_priv = to_i915(crtc->dev);
>  	struct intel_crtc *intel_crtc = to_intel_crtc(crtc);
>  	struct intel_crtc_state *cstate = to_intel_crtc_state(crtc->state);
>  
> @@ -3662,9 +3665,7 @@ static void ilk_update_wm(struct drm_crtc *crtc)
>  		intel_wait_for_vblank(crtc->dev, intel_crtc->pipe);
>  	}
>  
> -	intel_crtc->wm.active.ilk = cstate->wm.optimal.ilk;
> -
> -	ilk_program_watermarks(dev_priv);
> +	ilk_program_watermarks(cstate);
>  }
>  
>  static void skl_pipe_wm_active_state(uint32_t val,
> @@ -6972,6 +6973,7 @@ void intel_init_pm(struct drm_device *dev)
>  		     dev_priv->wm.spr_latency[0] && dev_priv->wm.cur_latency[0])) {
>  			dev_priv->display.update_wm = ilk_update_wm;
>  			dev_priv->display.compute_pipe_wm = ilk_compute_pipe_wm;
> +			dev_priv->display.program_watermarks = ilk_program_watermarks;
>  		} else {
>  			DRM_DEBUG_KMS("Failed to read display plane latency. "
>  				      "Disable CxSR\n");

-- 
Jani Nikula, Intel Open Source Technology Center
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