drm/i915: Program GMBUS Frequency based on the CDCLK for VLV.

CDCLK is used to generate the gmbus clock.  This is normally done by
BIOS. Program the value if the BIOS-less system doesn't do it.

v2: Move this to intel_i2c_reset to allow reprogram the gmbus frequency
during resume. (Daniel)

v3: Change GMBUS_FREQ to GMBUSFREQ_VLV, and use VLV_DISPLAY_BASE.
(Ville).
	Remove cdclk_ratio[] table, and calculate the cdclk ratio instead.
(Ville).
 	Change the shift then mask for reg read, to mask first, then shift.
(Ville).
	Remove the gmbus frequency calculation = cdclk/1.01.  Based on BIOS
programming, gmbus frequency = cdclk frequency. (Ville)
	Add get_disp_clk_div, which can use to get cdclk/czclk divide.

v4: Fix the mmio_offset base for CZCLK_CDCLK_FREQ_RATIO, gmbus_freq
calculation, and duplicate check for gmbus_freq. (Ville)

In VLV, the spec is wrong about 4Mhz reference frequency for GMBUS. It
should be 1Mhz.
Signed-off-by: Chon Ming Lee <chon.ming.lee@intel.com>
[danvet: Add the comment Ville suggested. Also appease checkpatch a
bit.]
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_reg.h

@@ -382,6 +382,8 @@
 #define   FB_FMAX_VMIN_FREQ_LO_MASK		0xf8000000
 
 /* vlv2 north clock has */
+#define CCK_FUSE_REG				0x8
+#define  CCK_FUSE_HPLL_FREQ_MASK		0x3
 #define CCK_REG_DSI_PLL_FUSE			0x44
 #define CCK_REG_DSI_PLL_CONTROL			0x48
 #define  DSI_PLL_VCO_EN				(1 << 31)
@@ -1429,6 +1431,12 @@
 
 #define MI_ARB_VLV		(VLV_DISPLAY_BASE + 0x6504)
 
+#define CZCLK_CDCLK_FREQ_RATIO	(VLV_DISPLAY_BASE + 0x6508)
+#define   CDCLK_FREQ_SHIFT	4
+#define   CDCLK_FREQ_MASK	(0x1f << CDCLK_FREQ_SHIFT)
+#define   CZCLK_FREQ_MASK	0xf
+#define GMBUSFREQ_VLV		(VLV_DISPLAY_BASE + 0x6510)
+
 /*
  * Palette regs
  */

drivers/gpu/drm/i915/intel_i2c.c

@@ -34,6 +34,11 @@
 #include <drm/i915_drm.h>
 #include "i915_drv.h"
 
+enum disp_clk {
+	CDCLK,
+	CZCLK
+};
+
 struct gmbus_port {
 	const char *name;
 	int reg;
@@ -58,10 +63,69 @@ to_intel_gmbus(struct i2c_adapter *i2c)
 	return container_of(i2c, struct intel_gmbus, adapter);
 }
 
+static int get_disp_clk_div(struct drm_i915_private *dev_priv,
+			    enum disp_clk clk)
+{
+	u32 reg_val;
+	int clk_ratio;
+
+	reg_val = I915_READ(CZCLK_CDCLK_FREQ_RATIO);
+
+	if (clk == CDCLK)
+		clk_ratio =
+			((reg_val & CDCLK_FREQ_MASK) >> CDCLK_FREQ_SHIFT) + 1;
+	else
+		clk_ratio = (reg_val & CZCLK_FREQ_MASK) + 1;
+
+	return clk_ratio;
+}
+
+static void gmbus_set_freq(struct drm_i915_private *dev_priv)
+{
+	int vco_freq[] = { 800, 1600, 2000, 2400 };
+	int gmbus_freq = 0, cdclk_div, hpll_freq;
+
+	BUG_ON(!IS_VALLEYVIEW(dev_priv->dev));
+
+	/* Skip setting the gmbus freq if BIOS has already programmed it */
+	if (I915_READ(GMBUSFREQ_VLV) != 0xA0)
+		return;
+
+	/* Obtain SKU information */
+	mutex_lock(&dev_priv->dpio_lock);
+	hpll_freq =
+		vlv_cck_read(dev_priv, CCK_FUSE_REG) & CCK_FUSE_HPLL_FREQ_MASK;
+	mutex_unlock(&dev_priv->dpio_lock);
+
+	/* Get the CDCLK divide ratio */
+	cdclk_div = get_disp_clk_div(dev_priv, CDCLK);
+
+	/*
+	 * Program the gmbus_freq based on the cdclk frequency.
+	 * BSpec erroneously claims we should aim for 4MHz, but
+	 * in fact 1MHz is the correct frequency.
+	 */
+	if (cdclk_div)
+		gmbus_freq = (vco_freq[hpll_freq] << 1) / cdclk_div;
+
+	if (WARN_ON(gmbus_freq == 0))
+		return;
+
+	I915_WRITE(GMBUSFREQ_VLV, gmbus_freq);
+}
+
 void
 intel_i2c_reset(struct drm_device *dev)
 {
 	struct drm_i915_private *dev_priv = dev->dev_private;
+
+	/*
+	 * In BIOS-less system, program the correct gmbus frequency
+	 * before reading edid.
+	 */
+	if (IS_VALLEYVIEW(dev))
+		gmbus_set_freq(dev_priv);
+
 	I915_WRITE(dev_priv->gpio_mmio_base + GMBUS0, 0);
 	I915_WRITE(dev_priv->gpio_mmio_base + GMBUS4, 0);
 }