[Intel-gfx] [PATCH 1/1] drm/i915: Implement workaround for CDCLK PLL disable/enable

[Srivatsa, Anusha]

> -----Original Message-----
> From: Intel-gfx <intel-gfx-bounces at lists.freedesktop.org> On Behalf Of
> Stanislav Lisovskiy
> Sent: Thursday, November 24, 2022 2:36 AM
> To: intel-gfx at lists.freedesktop.org
> Cc: Nikula, Jani <jani.nikula at intel.com>
> Subject: [Intel-gfx] [PATCH 1/1] drm/i915: Implement workaround for CDCLK
> PLL disable/enable
> 
> It was reported that we might get a hung and loss of register access in some
> cases when CDCLK PLL is disabled and then enabled, while squashing is
> enabled.
> As a workaround it was proposed by HW team that SW should disable
> squashing when CDCLK PLL is being reenabled.
> 
> Signed-off-by: Stanislav Lisovskiy <stanislav.lisovskiy at intel.com>
> ---
>  drivers/gpu/drm/i915/display/intel_cdclk.c | 14 ++++++++++++--
>  1 file changed, 12 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_cdclk.c
> b/drivers/gpu/drm/i915/display/intel_cdclk.c
> index 0c107a38f9d0..e338f288c9ac 100644
> --- a/drivers/gpu/drm/i915/display/intel_cdclk.c
> +++ b/drivers/gpu/drm/i915/display/intel_cdclk.c
> @@ -1801,6 +1801,13 @@ static bool
> cdclk_compute_crawl_and_squash_midpoint(struct drm_i915_private *i91
>  	return true;
>  }
> 
> +static bool pll_enable_wa_needed(struct drm_i915_private *dev_priv) {
> +	return ((IS_DG2(dev_priv) || IS_METEORLAKE(dev_priv))
> +		&& dev_priv->display.cdclk.hw.vco > 0
> +		&& HAS_CDCLK_SQUASH(dev_priv));
Redundant check. If it is MTL or DG2, then it will have HAS_CDCLK_SQUASH set to true always. Shouldn't vco be 0 instead of > 0. The commit message says the hang can be observed when moving from 0 to > 0 vco. 

Anusha
> +}
> +
>  static void _bxt_set_cdclk(struct drm_i915_private *dev_priv,
>  			   const struct intel_cdclk_config *cdclk_config,
>  			   enum pipe pipe)
> @@ -1815,9 +1822,12 @@ static void _bxt_set_cdclk(struct
> drm_i915_private *dev_priv,
>  	    !cdclk_pll_is_unknown(dev_priv->display.cdclk.hw.vco)) {
>  		if (dev_priv->display.cdclk.hw.vco != vco)
>  			adlp_cdclk_pll_crawl(dev_priv, vco);
> -	} else if (DISPLAY_VER(dev_priv) >= 11)
> +	} else if (DISPLAY_VER(dev_priv) >= 11) {
> +		if (pll_enable_wa_needed(dev_priv))
> +			dg2_cdclk_squash_program(dev_priv, 0);
> +
>  		icl_cdclk_pll_update(dev_priv, vco);
> -	else
> +	} else
>  		bxt_cdclk_pll_update(dev_priv, vco);
> 
>  	waveform = cdclk_squash_waveform(dev_priv, cdclk);
> --
> 2.37.3