drm/i915: Polish skl_is_16gb_dimm()

Pass the dimm struct to skl_is_16gb_dimm() rather than passing each
value separately. And let's replace the hardcoded set of values with
some simple arithmetic.

Also fix the byte vs. bit inconsistency in the debug message,
and polish the wording otherwise as well.

v2: Deobfuscate the math (Chris)
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190306203551.24592-4-ville.syrjala@linux.intel.com

drivers/gpu/drm/i915/i915_drv.c

@@ -1068,6 +1068,11 @@ static void intel_sanitize_options(struct drm_i915_private *dev_priv)
 	intel_gvt_sanitize_options(dev_priv);
 }
 
+static int intel_dimm_num_devices(const struct dram_dimm_info *dimm)
+{
+	return dimm->ranks * 64 / (dimm->width ?: 1);
+}
+
 /* Returns total GB for the whole DIMM */
 static int skl_get_dimm_size(u16 val)
 {
@@ -1102,18 +1107,10 @@ static int skl_get_dimm_ranks(u16 val)
 }
 
 static bool
-skl_is_16gb_dimm(u8 ranks, u8 size, u8 width)
+skl_is_16gb_dimm(const struct dram_dimm_info *dimm)
 {
-	if (ranks == 1 && width == 8 && size == 16)
-		return true;
-	else if (ranks == 2 && width == 8 && size == 32)
-		return true;
-	else if (ranks == 1 && width == 16 && size == 8)
-		return true;
-	else if (ranks == 2 && width == 16 && size == 16)
-		return true;
-
-	return false;
+	/* Convert total GB to Gb per DRAM device */
+	return 8 * dimm->size / (intel_dimm_num_devices(dimm) ?: 1) == 16;
 }
 
 static int
@@ -1143,10 +1140,9 @@ skl_dram_get_channel_info(struct dram_channel_info *ch, u32 val)
 	else
 		ch->ranks = 1;
 
-	ch->is_16gb_dimm = skl_is_16gb_dimm(ch->l_info.ranks, ch->l_info.size,
-					    ch->l_info.width) ||
-			   skl_is_16gb_dimm(ch->s_info.ranks, ch->s_info.size,
-					    ch->s_info.width);
+	ch->is_16gb_dimm =
+		skl_is_16gb_dimm(&ch->l_info) ||
+		skl_is_16gb_dimm(&ch->s_info);
 
 	DRM_DEBUG_KMS("(size:width:ranks) L(%uGB:X%u:%u) S(%uGB:X%u:%u)\n",
 		      ch->l_info.size, ch->l_info.width, ch->l_info.ranks,
@@ -1364,7 +1360,7 @@ 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 ranks: %u, 16GB-dimm:%s\n",
+	DRM_DEBUG_KMS("DRAM ranks: %u, 16Gb DIMMs: %s\n",
 		      dram_info->ranks, yesno(dram_info->is_16gb_dimm));
 }
 

drivers/gpu/drm/i915/i915_drv.h

@@ -2052,10 +2052,12 @@ struct drm_i915_private {
 	 */
 };
 
+struct dram_dimm_info {
+	u8 size, width, ranks;
+};
+
 struct dram_channel_info {
-	struct info {
-		u8 size, width, ranks;
-	} l_info, s_info;
+	struct dram_dimm_info l_info, s_info;
 	u8 ranks;
 	bool is_16gb_dimm;
 };