Re: [Intel-gfx] [PATCH] drm/i915/tgl: Program BW_BUDDY registers during display init

["Lisovskiy, Stanislav" <stanislav.lisovskiy@intel.com>]

On Wed, 2019-12-04 at 12:51 -0800, Matt Roper wrote:
> Gen12 can improve bandwidth efficiency by pairing up memory requests
> with similar addresses.  We need to program the BW_BUDDY1 and
> BW_BUDDY2
> registers according to the memory configuration during display
> initialization to take advantage of this capability.
> 
> The magic numbers we program here feel like something that could
> definitely change on future platforms, so let's use a table-based
> programming scheme to make this easy to extend in the future.
> 
> Bspec: 49189
> Bspec: 49218
> Cc: Stanislav Lisovskiy <stanislav.lisovskiy@intel.com>
> Cc: Ville Syrjala <ville.syrjala@linux.intel.com>
> Cc: Lucas De Marchi <lucas.demarchi@intel.com>
> Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
> ---
>  .../drm/i915/display/intel_display_power.c    | 40
> +++++++++++++++++++
>  drivers/gpu/drm/i915/i915_reg.h               |  8 ++++
>  2 files changed, 48 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_display_power.c
> b/drivers/gpu/drm/i915/display/intel_display_power.c
> index ce1b64f4dd44..1d26f741b5b4 100644
> --- a/drivers/gpu/drm/i915/display/intel_display_power.c
> +++ b/drivers/gpu/drm/i915/display/intel_display_power.c
> @@ -4781,6 +4781,42 @@ static void cnl_display_core_uninit(struct
> drm_i915_private *dev_priv)
>  	intel_combo_phy_uninit(dev_priv);
>  }
>  
> +struct buddy_page_mask {
> +	u8 num_channels;
> +	enum intel_dram_type type;
> +	u32 page_mask;
> +};
> +
> +const struct buddy_page_mask tgl_buddy_page_masks[] = {
> +	{ 1, INTEL_DRAM_LPDDR4, 0xE },
> +	{ 1, INTEL_DRAM_DDR4,   0xF },
> +	{ 2, INTEL_DRAM_LPDDR4, 0x1C },
> +	{ 2, INTEL_DRAM_DDR4,   0x1F },
> +	{}
> +};
> +
> +static void tgl_arbiter_init(struct drm_i915_private *dev_priv)
> +{
> +	enum intel_dram_type type = dev_priv->dram_info.type;
> +	u8 num_channels = dev_priv->dram_info.num_channels;
> +	const struct buddy_page_mask *table = tgl_buddy_page_masks;
> +	int i;
> +
> +	for (i = 0; table[i].page_mask != 0; i++)
> +		if (table[i].num_channels == num_channels &&
> +		    table[i].type == type)
> +			break;
> +
> +	if (table[i].page_mask == 0) {
> +		DRM_DEBUG_DRIVER("Unknown memory configuration;
> disabling address buddy logic.\n");
> +		I915_WRITE(BW_BUDDY1_CTL, BW_BUDDY_DISABLE);
> +		I915_WRITE(BW_BUDDY2_CTL, BW_BUDDY_DISABLE);
> +	} else {
> +		I915_WRITE(BW_BUDDY1_PAGE_MASK, table[i].page_mask);
> +		I915_WRITE(BW_BUDDY2_PAGE_MASK, table[i].page_mask);
> +	}
> +}

Great idea to implement this, I already had actually patch for that
for almost a month as were using it for joint debug with Windows team,
but was a bit in a doubt whether I can send it because of secrecy
issues. 

However there is one more thing: it seems that what that there is
already a workaround (check BSpec workaround 1409767108), which
instructs to set up those in a completely different way from what has
been set in BSpec initially.

Stan

> +
>  static void icl_display_core_init(struct drm_i915_private *dev_priv,
>  				  bool resume)
>  {
> @@ -4813,6 +4849,10 @@ static void icl_display_core_init(struct
> drm_i915_private *dev_priv,
>  	/* 6. Setup MBUS. */
>  	icl_mbus_init(dev_priv);
>  
> +	/* 7. Program arbiter BW_BUDDY registers */
> +	if (INTEL_GEN(dev_priv) >= 12)
> +		tgl_arbiter_init(dev_priv);
> +
>  	if (resume && dev_priv->csr.dmc_payload)
>  		intel_csr_load_program(dev_priv);
>  }
> diff --git a/drivers/gpu/drm/i915/i915_reg.h
> b/drivers/gpu/drm/i915/i915_reg.h
> index 1a6376a97d48..082190c2dc48 100644
> --- a/drivers/gpu/drm/i915/i915_reg.h
> +++ b/drivers/gpu/drm/i915/i915_reg.h
> @@ -7765,6 +7765,14 @@ enum {
>  #define GEN7_MSG_CTL	_MMIO(0x45010)
>  #define  WAIT_FOR_PCH_RESET_ACK		(1 << 1)
>  #define  WAIT_FOR_PCH_FLR_ACK		(1 << 0)
> +
> +#define BW_BUDDY1_CTL			_MMIO(0x45140)
> +#define BW_BUDDY2_CTL			_MMIO(0x45150)
> +#define   BW_BUDDY_DISABLE		REG_BIT(31)
> +
> +#define BW_BUDDY1_PAGE_MASK		_MMIO(0x45144)
> +#define BW_BUDDY2_PAGE_MASK		_MMIO(0x45154)
> +
>  #define HSW_NDE_RSTWRN_OPT	_MMIO(0x46408)
>  #define  RESET_PCH_HANDSHAKE_ENABLE	(1 << 4)
>  
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