Re: [PATCH 3/5] drm/i915: Implement 16GB dimm wa for latency level-0

[Rodrigo Vivi <rodrigo.vivi@intel.com>]

On Thu, Jul 26, 2018 at 07:44:08PM +0530, Mahesh Kumar wrote:
> Memory with 16GB dimms require an increase of 1us in level-0 latency.
> This patch implements the same.
> Bspec: 4381
> 
> changes since V1:
>  - s/memdev_info/dram_info
>  - make skl_is_16gb_dimm pure function
> 
> Signed-off-by: Mahesh Kumar <mahesh1.kumar@intel.com>
> ---
>  drivers/gpu/drm/i915/i915_drv.c | 40 ++++++++++++++++++++++++++++++++++++++--
>  drivers/gpu/drm/i915/i915_drv.h |  3 +++
>  drivers/gpu/drm/i915/intel_pm.c | 13 +++++++++++++
>  3 files changed, 54 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_drv.c b/drivers/gpu/drm/i915/i915_drv.c
> index ddf6bf9b500a..86bc2e685522 100644
> --- a/drivers/gpu/drm/i915/i915_drv.c
> +++ b/drivers/gpu/drm/i915/i915_drv.c
> @@ -1070,6 +1070,25 @@ static void intel_sanitize_options(struct drm_i915_private *dev_priv)
>  	intel_gvt_sanitize_options(dev_priv);
>  }
>  
> +static bool
> +skl_is_16gb_dimm(u8 rank, u8 size, u8 width)
> +{
> +	if (size == 16 && width == SKL_DRAM_WIDTH_X8 &&
> +	    rank == SKL_DRAM_RANK_SINGLE)
> +		return true;
> +	else if (size == 32 && width == SKL_DRAM_WIDTH_X8 &&
> +		 rank == SKL_DRAM_RANK_DUAL)
> +		return true;
> +	else if (size == 8 && width == SKL_DRAM_WIDTH_X16 &&
> +		 rank == SKL_DRAM_RANK_SINGLE)
> +		return true;
> +	else if (size == 16 && width == SKL_DRAM_WIDTH_X16 &&
> +		 rank == SKL_DRAM_RANK_DUAL)
> +		return true;

nip: This is right, but it would be easier if order of checks
     were in same order as spec. Well.. but no real need for
     change since I already checked ;)

> +
> +	return false;
> +}
> +
>  static int
>  skl_dram_get_channel_info(struct dram_channel_info *ch, u32 val)
>  {
> @@ -1077,6 +1096,7 @@ skl_dram_get_channel_info(struct dram_channel_info *ch, u32 val)
>  	u8 l_size, s_size;
>  	u8 l_width, s_width;
>  	enum dram_rank rank;
> +	bool l_16gb_dimm, s_16gb_dimm;

I don't think we need this extra locals

>  
>  	if (!val)
>  		return -1;
> @@ -1103,6 +1123,13 @@ skl_dram_get_channel_info(struct dram_channel_info *ch, u32 val)
>  	else
>  		rank = I915_DRAM_RANK_SINGLE;
>  
> +	l_16gb_dimm = skl_is_16gb_dimm(l_rank, l_size, l_width);
> +	s_16gb_dimm = skl_is_16gb_dimm(s_rank, s_size, s_width);
> +
> +	if (l_16gb_dimm || s_16gb_dimm)
> +		ch->is_16gb_dimm = true;
> +	else
> +		ch->is_16gb_dimm = false;
	ch->is_16gb_dim = skl_is_16gb_dimm(l_rank, l_size, l_width) ||
			  skl_is_16gb_dimm(s_rank, s_size, s_width);

>  	ch->l_info.size = l_size;
>  	ch->s_info.size = s_size;
>  	ch->l_info.width = l_width;
> @@ -1137,6 +1164,8 @@ skl_dram_get_channels_info(struct drm_i915_private *dev_priv)
>  		return -EINVAL;
>  	}
>  
> +	dram_info->valid_dimm = true;
> +
>  	/*
>  	 * If any of the channel is single rank channel, worst case output
>  	 * will be same as if single rank memory, so consider single rank
> @@ -1152,6 +1181,10 @@ skl_dram_get_channels_info(struct drm_i915_private *dev_priv)
>  		DRM_INFO("couldn't get memory rank information\n");
>  		return -EINVAL;
>  	}
> +
> +	if (ch0.is_16gb_dimm || ch1.is_16gb_dimm)
> +		dram_info->is_16gb_dimm = true;
> +
>  	return 0;
>  }
>  
> @@ -1263,6 +1296,7 @@ bxt_get_dram_info(struct drm_i915_private *dev_priv)
>  		return -EINVAL;
>  	}
>  
> +	dram_info->valid_dimm = true;
>  	dram_info->valid = true;
>  	return 0;
>  }
> @@ -1275,6 +1309,8 @@ intel_get_dram_info(struct drm_i915_private *dev_priv)
>  	int ret;
>  
>  	dram_info->valid = false;
> +	dram_info->valid_dimm = false;
> +	dram_info->is_16gb_dimm = false;
>  	dram_info->rank = I915_DRAM_RANK_INVALID;
>  	dram_info->bandwidth_kbps = 0;
>  	dram_info->num_channels = 0;
> @@ -1298,9 +1334,9 @@ intel_get_dram_info(struct drm_i915_private *dev_priv)
>  		sprintf(bandwidth_str, "unknown");
>  	DRM_DEBUG_KMS("DRAM bandwidth:%s, total-channels: %u\n",
>  		      bandwidth_str, dram_info->num_channels);
> -	DRM_DEBUG_KMS("DRAM rank: %s rank\n",
> +	DRM_DEBUG_KMS("DRAM rank: %s rank 16GB-dimm:%s\n",
>  		      (dram_info->rank == I915_DRAM_RANK_DUAL) ?
> -		      "dual" : "single");
> +		      "dual" : "single", yesno(dram_info->is_16gb_dimm));
>  }
>  
>  /**
> diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
> index 2d12fc152b49..854f3c828e01 100644
> --- a/drivers/gpu/drm/i915/i915_drv.h
> +++ b/drivers/gpu/drm/i915/i915_drv.h
> @@ -1906,6 +1906,8 @@ struct drm_i915_private {
>  
>  	struct dram_info {
>  		bool valid;
> +		bool valid_dimm;
> +		bool is_16gb_dimm;
>  		u8 num_channels;
>  		enum dram_rank {
>  			I915_DRAM_RANK_INVALID = 0,
> @@ -2133,6 +2135,7 @@ struct dram_channel_info {
>  		u8 size, width, rank;
>  	} l_info, s_info;
>  	enum dram_rank rank;
> +	bool is_16gb_dimm;
>  };
>  
>  static inline struct drm_i915_private *to_i915(const struct drm_device *dev)
> diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
> index 7312ecb73415..2446f53adf21 100644
> --- a/drivers/gpu/drm/i915/intel_pm.c
> +++ b/drivers/gpu/drm/i915/intel_pm.c
> @@ -2874,6 +2874,19 @@ static void intel_read_wm_latency(struct drm_i915_private *dev_priv,
>  			}
>  		}
>  
> +		/*
> +		 * WA Level-0 adjustment for 16GB DIMMs: SKL+
> +		 * If we could not get dimm info enable this WA to prevent from
> +		 * any underrun. If not able to get Dimm info assume 16GB dimm
> +		 * to avoid any underrun.
> +		 */
> +		if (dev_priv->dram_info.valid_dimm) {
> +			if (dev_priv->dram_info.is_16gb_dimm)
> +				wm[0] += 1;
> +		} else {
> +			wm[0] += 1;

well... spec don't cover this case... I believe it is safe,
but only concern would be this creating latency for other cases...
just thinking loud, but I'm probably in favor of doing this anyway...

> +		}
> +
>  	} else if (IS_HASWELL(dev_priv) || IS_BROADWELL(dev_priv)) {
>  		uint64_t sskpd = I915_READ64(MCH_SSKPD);
>  
> -- 
> 2.16.2
> 
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