Re: [PATCH v4 09/11] drm/i915/mtl: Update MBUS_DBOX credits

[Matt Roper <matthew.d.roper@intel.com>]

On Thu, Sep 01, 2022 at 11:03:40PM -0700, Radhakrishna Sripada wrote:
> Display version 14 platforms have different credits values
> compared to ADL-P. Update the credits based on pipe usage.
> 
> v2: Simplify DBOX BW Credit definition(MattR)
> 
> Bspec: 49213
> 
> Cc: Jose Roberto de Souza <jose.souza@intel.com>
> Cc: Matt Roper <matthew.d.roper@intel.com>
> Original Author: Caz Yokoyama
> Signed-off-by: José Roberto de Souza <jose.souza@intel.com>
> Signed-off-by: Radhakrishna Sripada <radhakrishna.sripada@intel.com>
> ---
>  drivers/gpu/drm/i915/i915_reg.h |  4 +++
>  drivers/gpu/drm/i915/intel_pm.c | 47 ++++++++++++++++++++++++++++++---
>  2 files changed, 47 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_reg.h b/drivers/gpu/drm/i915/i915_reg.h
> index d22fabe35a0c..f9237586ab4f 100644
> --- a/drivers/gpu/drm/i915/i915_reg.h
> +++ b/drivers/gpu/drm/i915/i915_reg.h
> @@ -1125,8 +1125,12 @@
>  #define MBUS_DBOX_REGULATE_B2B_TRANSACTIONS_EN	REG_BIT(16) /* tgl+ */
>  #define MBUS_DBOX_BW_CREDIT_MASK		REG_GENMASK(15, 14)
>  #define MBUS_DBOX_BW_CREDIT(x)			REG_FIELD_PREP(MBUS_DBOX_BW_CREDIT_MASK, x)
> +#define MBUS_DBOX_BW_4CREDITS_MTL		REG_FIELD_PREP(MBUS_DBOX_BW_CREDIT_MASK, 0x2)
> +#define MBUS_DBOX_BW_8CREDITS_MTL		REG_FIELD_PREP(MBUS_DBOX_BW_CREDIT_MASK, 0x3)
>  #define MBUS_DBOX_B_CREDIT_MASK			REG_GENMASK(12, 8)
>  #define MBUS_DBOX_B_CREDIT(x)			REG_FIELD_PREP(MBUS_DBOX_B_CREDIT_MASK, x)
> +#define MBUS_DBOX_I_CREDIT_MASK			REG_GENMASK(7, 5)
> +#define MBUS_DBOX_I_CREDIT(x)			REG_FIELD_PREP(MBUS_DBOX_I_CREDIT_MASK, x)
>  #define MBUS_DBOX_A_CREDIT_MASK			REG_GENMASK(3, 0)
>  #define MBUS_DBOX_A_CREDIT(x)			REG_FIELD_PREP(MBUS_DBOX_A_CREDIT_MASK, x)
>  
> diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
> index ebce6171ccef..b19a1ecb010e 100644
> --- a/drivers/gpu/drm/i915/intel_pm.c
> +++ b/drivers/gpu/drm/i915/intel_pm.c
> @@ -8448,6 +8448,27 @@ void intel_dbuf_post_plane_update(struct intel_atomic_state *state)
>  				new_dbuf_state->enabled_slices);
>  }
>  
> +static bool xelpdp_is_one_pipe_per_dbuf_bank(enum pipe pipe, u8 active_pipes)

Bikeshed:  s/one/only/ might be slightly more clear?

> +{
> +	switch (pipe) {
> +	case PIPE_A:
> +	case PIPE_D:
> +		if (is_power_of_2(active_pipes & (BIT(PIPE_A) | BIT(PIPE_D))))

Bikeshed:  writing this with hweight might be more intuitive than
power_of_2?  Or even just a direct check of the other pipe like

        case PIPE_A:
                return !(active_pipes & BIT(PIPE_D))
        case PIPE_D:
                return !(active_pipes & BIT(PIPE_A))
        ...

> +			return true;
> +		break;
> +	case PIPE_B:
> +	case PIPE_C:
> +		if (is_power_of_2(active_pipes & (BIT(PIPE_B) | BIT(PIPE_C))))
> +			return true;
> +		break;
> +	default: /* to suppress compiler warning */
> +		MISSING_CASE(pipe);
> +		break;
> +	}
> +
> +	return false;
> +}
> +
>  void intel_mbus_dbox_update(struct intel_atomic_state *state)
>  {
>  	struct drm_i915_private *i915 = to_i915(state->base.dev);
> @@ -8467,20 +8488,28 @@ void intel_mbus_dbox_update(struct intel_atomic_state *state)
>  	     new_dbuf_state->active_pipes == old_dbuf_state->active_pipes))
>  		return;
>  
> +	if (DISPLAY_VER(i915) >= 14)
> +		val |= MBUS_DBOX_I_CREDIT(2);
> +
>  	if (DISPLAY_VER(i915) >= 12) {
>  		val |= MBUS_DBOX_B2B_TRANSACTIONS_MAX(16);
>  		val |= MBUS_DBOX_B2B_TRANSACTIONS_DELAY(1);
>  		val |= MBUS_DBOX_REGULATE_B2B_TRANSACTIONS_EN;
>  	}
>  
> -	/* Wa_22010947358:adl-p */
> -	if (IS_ALDERLAKE_P(i915))
> +	if (DISPLAY_VER(i915) >= 14)
> +		val |= new_dbuf_state->joined_mbus ? MBUS_DBOX_A_CREDIT(12) :
> +						     MBUS_DBOX_A_CREDIT(8);
> +	else if (IS_ALDERLAKE_P(i915))
> +		/* Wa_22010947358:adl-p */
>  		val |= new_dbuf_state->joined_mbus ? MBUS_DBOX_A_CREDIT(6) :
>  						     MBUS_DBOX_A_CREDIT(4);
>  	else
>  		val |= MBUS_DBOX_A_CREDIT(2);
>  
> -	if (IS_ALDERLAKE_P(i915)) {
> +	if (DISPLAY_VER(i915) >= 14) {
> +		val |= MBUS_DBOX_B_CREDIT(0xA);
> +	} else if (IS_ALDERLAKE_P(i915)) {
>  		val |= MBUS_DBOX_BW_CREDIT(2);
>  		val |= MBUS_DBOX_B_CREDIT(8);
>  	} else if (DISPLAY_VER(i915) >= 12) {
> @@ -8492,10 +8521,20 @@ void intel_mbus_dbox_update(struct intel_atomic_state *state)
>  	}
>  
>  	for_each_new_intel_crtc_in_state(state, crtc, new_crtc_state, i) {
> +		u32 pipe_val = val;
> +
>  		if (!new_crtc_state->hw.active ||
>  		    !intel_crtc_needs_modeset(new_crtc_state))
>  			continue;

What if the number of BW credits for a pipe changes when this pipe
itself isn't undergoing a modeset?  E.g., what if you initially had pipe
A active as the only pipe and thus programmed 8 BW credits.  Then you
turn on pipe D; since we're not touching pipe A directly we skip any
programming here (leaving it at 8 credits) and only program the 4
credits for pipe D's instance of the register.  Am I missing something
here?


Matt

>  
> -		intel_de_write(i915, PIPE_MBUS_DBOX_CTL(crtc->pipe), val);
> +		if (DISPLAY_VER(i915) >= 14) {
> +			if (xelpdp_is_one_pipe_per_dbuf_bank(crtc->pipe,
> +							     new_dbuf_state->active_pipes))
> +				pipe_val |= MBUS_DBOX_BW_8CREDITS_MTL;
> +			else
> +				pipe_val |= MBUS_DBOX_BW_4CREDITS_MTL;
> +		}
> +
> +		intel_de_write(i915, PIPE_MBUS_DBOX_CTL(crtc->pipe), pipe_val);
>  	}
>  }
> -- 
> 2.34.1
> 

-- 
Matt Roper
Graphics Software Engineer
VTT-OSGC Platform Enablement
Intel Corporation