drm/i915: Invert if/else ladder for frequency read

Continue converting the driver to the convention of last version first,
extending it to the future platforms. Now, any GRAPHICS_VER >= 11 will
be handled by the first branch.

With the new ranges it's easier to see what platform a branch started to
be taken. Besides the >= 11 change, the branch taken for GRAPHICS_VER == 10
is also different, but currently there is no such platform in i915.
Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>
Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220908-if-ladder-v2-1-7a7b15545c93@intel.com

drivers/gpu/drm/i915/gt/intel_gt_clock_utils.c

@@ -78,77 +78,74 @@ static u32 read_clock_frequency(struct intel_uncore *uncore)
 	u32 f19_2_mhz = 19200000;
 	u32 f24_mhz = 24000000;
 
-	if (GRAPHICS_VER(uncore->i915) <= 4) {
-		/*
-		 * PRMs say:
-		 *
-		 *     "The value in this register increments once every 16
-		 *      hclks." (through the “Clocking Configuration”
-		 *      (“CLKCFG”) MCHBAR register)
-		 */
-		return RUNTIME_INFO(uncore->i915)->rawclk_freq * 1000 / 16;
-	} else if (GRAPHICS_VER(uncore->i915) <= 8) {
-		/*
-		 * PRMs say:
-		 *
-		 *     "The PCU TSC counts 10ns increments; this timestamp
-		 *      reflects bits 38:3 of the TSC (i.e. 80ns granularity,
-		 *      rolling over every 1.5 hours).
-		 */
-		return f12_5_mhz;
-	} else if (GRAPHICS_VER(uncore->i915) <= 9) {
+	if (GRAPHICS_VER(uncore->i915) >= 11) {
 		u32 ctc_reg = intel_uncore_read(uncore, CTC_MODE);
 		u32 freq = 0;
 
+		/*
+		 * First figure out the reference frequency. There are 2 ways
+		 * we can compute the frequency, either through the
+		 * TIMESTAMP_OVERRIDE register or through RPM_CONFIG. CTC_MODE
+		 * tells us which one we should use.
+		 */
 		if ((ctc_reg & CTC_SOURCE_PARAMETER_MASK) == CTC_SOURCE_DIVIDE_LOGIC) {
 			freq = read_reference_ts_freq(uncore);
 		} else {
-			freq = IS_GEN9_LP(uncore->i915) ? f19_2_mhz : f24_mhz;
+			u32 c0 = intel_uncore_read(uncore, RPM_CONFIG0);
+
+			if (GRAPHICS_VER(uncore->i915) >= 11)
+				freq = gen11_get_crystal_clock_freq(uncore, c0);
+			else
+				freq = gen9_get_crystal_clock_freq(uncore, c0);
 
 			/*
 			 * Now figure out how the command stream's timestamp
 			 * register increments from this frequency (it might
 			 * increment only every few clock cycle).
 			 */
-			freq >>= 3 - ((ctc_reg & CTC_SHIFT_PARAMETER_MASK) >>
-				      CTC_SHIFT_PARAMETER_SHIFT);
+			freq >>= 3 - ((c0 & GEN10_RPM_CONFIG0_CTC_SHIFT_PARAMETER_MASK) >>
+				      GEN10_RPM_CONFIG0_CTC_SHIFT_PARAMETER_SHIFT);
 		}
 
 		return freq;
-	} else if (GRAPHICS_VER(uncore->i915) <= 12) {
+	} else if (GRAPHICS_VER(uncore->i915) >= 9) {
 		u32 ctc_reg = intel_uncore_read(uncore, CTC_MODE);
 		u32 freq = 0;
 
-		/*
-		 * First figure out the reference frequency. There are 2 ways
-		 * we can compute the frequency, either through the
-		 * TIMESTAMP_OVERRIDE register or through RPM_CONFIG. CTC_MODE
-		 * tells us which one we should use.
-		 */
 		if ((ctc_reg & CTC_SOURCE_PARAMETER_MASK) == CTC_SOURCE_DIVIDE_LOGIC) {
 			freq = read_reference_ts_freq(uncore);
 		} else {
-			u32 c0 = intel_uncore_read(uncore, RPM_CONFIG0);
-
-			if (GRAPHICS_VER(uncore->i915) >= 11)
-				freq = gen11_get_crystal_clock_freq(uncore, c0);
-			else
-				freq = gen9_get_crystal_clock_freq(uncore, c0);
+			freq = IS_GEN9_LP(uncore->i915) ? f19_2_mhz : f24_mhz;
 
 			/*
 			 * Now figure out how the command stream's timestamp
 			 * register increments from this frequency (it might
 			 * increment only every few clock cycle).
 			 */
-			freq >>= 3 - ((c0 & GEN10_RPM_CONFIG0_CTC_SHIFT_PARAMETER_MASK) >>
-				      GEN10_RPM_CONFIG0_CTC_SHIFT_PARAMETER_SHIFT);
+			freq >>= 3 - ((ctc_reg & CTC_SHIFT_PARAMETER_MASK) >>
+				      CTC_SHIFT_PARAMETER_SHIFT);
 		}
 
 		return freq;
+	} else if (GRAPHICS_VER(uncore->i915) >= 5) {
+		/*
+		 * PRMs say:
+		 *
+		 *     "The PCU TSC counts 10ns increments; this timestamp
+		 *      reflects bits 38:3 of the TSC (i.e. 80ns granularity,
+		 *      rolling over every 1.5 hours).
+		 */
+		return f12_5_mhz;
+	} else {
+		/*
+		 * PRMs say:
+		 *
+		 *     "The value in this register increments once every 16
+		 *      hclks." (through the “Clocking Configuration”
+		 *      (“CLKCFG”) MCHBAR register)
+		 */
+		return RUNTIME_INFO(uncore->i915)->rawclk_freq * 1000 / 16;
 	}
-
-	MISSING_CASE("Unknown gen, unable to read command streamer timestamp frequency\n");
-	return 0;
 }
 
 void intel_gt_init_clock_frequency(struct intel_gt *gt)