drm/i915: split out i915_freq.[ch]

The i915 core only needs three rather specific functions from
soc/intel_dram.[ch]: i9xx_fsb_freq(), ilk_fsb_freq(), and
ilk_mem_freq(). Add new i915_freq.[ch] and duplicate those functions for
i915 to reduce the dependency on soc/ code.

Wile duplication in general is bad, here it's a tradeoff to simplify the
i915, xe and display interactions.

Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patch.msgid.link/7bac1b194afdc20cd45e625a0a32fcbcd0b1136e.1763578288.git.jani.nikula@intel.com
Signed-off-by: Jani Nikula <jani.nikula@intel.com>

drivers/gpu/drm/i915/Makefile

@@ -28,6 +28,7 @@ i915-y += \
 	i915_driver.o \
 	i915_drm_client.o \
 	i915_edram.o \
+	i915_freq.o \
 	i915_getparam.o \
 	i915_ioctl.o \
 	i915_irq.o \

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

@@ -4,12 +4,12 @@
  */
 
 #include "i915_drv.h"
+#include "i915_freq.h"
 #include "i915_reg.h"
 #include "intel_gt.h"
 #include "intel_gt_clock_utils.h"
 #include "intel_gt_print.h"
 #include "intel_gt_regs.h"
-#include "soc/intel_dram.h"
 
 static u32 read_reference_ts_freq(struct intel_uncore *uncore)
 {
@@ -148,7 +148,7 @@ static u32 gen4_read_clock_frequency(struct intel_uncore *uncore)
 	 *
 	 * Testing on actual hardware has shown there is no /16.
 	 */
-	return DIV_ROUND_CLOSEST(intel_fsb_freq(uncore->i915), 4) * 1000;
+	return DIV_ROUND_CLOSEST(i9xx_fsb_freq(uncore->i915), 4) * 1000;
 }
 
 static u32 read_clock_frequency(struct intel_uncore *uncore)

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

@@ -10,9 +10,9 @@
 
 #include "display/intel_display_rps.h"
 #include "display/vlv_clock.h"
-#include "soc/intel_dram.h"
 
 #include "i915_drv.h"
+#include "i915_freq.h"
 #include "i915_irq.h"
 #include "i915_reg.h"
 #include "i915_wait_util.h"
@@ -285,8 +285,8 @@ static void gen5_rps_init(struct intel_rps *rps)
 	u32 rgvmodectl;
 	int c_m, i;
 
-	fsb_freq = intel_fsb_freq(i915);
-	mem_freq = intel_mem_freq(i915);
+	fsb_freq = ilk_fsb_freq(i915);
+	mem_freq = ilk_mem_freq(i915);
 
 	if (fsb_freq <= 3200000)
 		c_m = 0;

drivers/gpu/drm/i915/i915_freq.c

@@ -0,0 +1,111 @@
+// SPDX-License-Identifier: MIT
+/* Copyright © 2025 Intel Corporation */
+
+#include <drm/drm_print.h>
+
+#include "i915_drv.h"
+#include "i915_freq.h"
+#include "intel_mchbar_regs.h"
+
+unsigned int i9xx_fsb_freq(struct drm_i915_private *i915)
+{
+	u32 fsb;
+
+	/*
+	 * Note that this only reads the state of the FSB
+	 * straps, not the actual FSB frequency. Some BIOSen
+	 * let you configure each independently. Ideally we'd
+	 * read out the actual FSB frequency but sadly we
+	 * don't know which registers have that information,
+	 * and all the relevant docs have gone to bit heaven :(
+	 */
+	fsb = intel_uncore_read(&i915->uncore, CLKCFG) & CLKCFG_FSB_MASK;
+
+	if (IS_PINEVIEW(i915) || IS_MOBILE(i915)) {
+		switch (fsb) {
+		case CLKCFG_FSB_400:
+			return 400000;
+		case CLKCFG_FSB_533:
+			return 533333;
+		case CLKCFG_FSB_667:
+			return 666667;
+		case CLKCFG_FSB_800:
+			return 800000;
+		case CLKCFG_FSB_1067:
+			return 1066667;
+		case CLKCFG_FSB_1333:
+			return 1333333;
+		default:
+			MISSING_CASE(fsb);
+			return 1333333;
+		}
+	} else {
+		switch (fsb) {
+		case CLKCFG_FSB_400_ALT:
+			return 400000;
+		case CLKCFG_FSB_533:
+			return 533333;
+		case CLKCFG_FSB_667:
+			return 666667;
+		case CLKCFG_FSB_800:
+			return 800000;
+		case CLKCFG_FSB_1067_ALT:
+			return 1066667;
+		case CLKCFG_FSB_1333_ALT:
+			return 1333333;
+		case CLKCFG_FSB_1600_ALT:
+			return 1600000;
+		default:
+			MISSING_CASE(fsb);
+			return 1333333;
+		}
+	}
+}
+
+unsigned int ilk_fsb_freq(struct drm_i915_private *i915)
+{
+	u16 fsb;
+
+	fsb = intel_uncore_read16(&i915->uncore, CSIPLL0) & 0x3ff;
+
+	switch (fsb) {
+	case 0x00c:
+		return 3200000;
+	case 0x00e:
+		return 3733333;
+	case 0x010:
+		return 4266667;
+	case 0x012:
+		return 4800000;
+	case 0x014:
+		return 5333333;
+	case 0x016:
+		return 5866667;
+	case 0x018:
+		return 6400000;
+	default:
+		drm_dbg(&i915->drm, "unknown fsb frequency 0x%04x\n", fsb);
+		return 0;
+	}
+}
+
+unsigned int ilk_mem_freq(struct drm_i915_private *i915)
+{
+	u16 ddrpll;
+
+	ddrpll = intel_uncore_read16(&i915->uncore, DDRMPLL1);
+	switch (ddrpll & 0xff) {
+	case 0xc:
+		return 800000;
+	case 0x10:
+		return 1066667;
+	case 0x14:
+		return 1333333;
+	case 0x18:
+		return 1600000;
+	default:
+		drm_dbg(&i915->drm, "unknown memory frequency 0x%02x\n",
+			ddrpll & 0xff);
+		return 0;
+	}
+}

drivers/gpu/drm/i915/i915_freq.h

@@ -0,0 +1,13 @@
+/* SPDX-License-Identifier: MIT */
+/* Copyright © 2025 Intel Corporation */
+
+#ifndef __I915_FREQ_H__
+#define __I915_FREQ_H__
+
+struct drm_i915_private;
+
+unsigned int i9xx_fsb_freq(struct drm_i915_private *i915);
+unsigned int ilk_fsb_freq(struct drm_i915_private *i915);
+unsigned int ilk_mem_freq(struct drm_i915_private *i915);
+
+#endif /* __I915_FREQ_H__ */