drm/i915: add support for SBI ops

With Lynx Point, we need to use SBI to communicate with the display clock
control. This commit adds helper functions to access the registers via
SBI.

v2: de-inline the function and address changes in bits names

v3: protect operations with dpio_lock, increase timeout to 100 for
paranoia sake.

v4: decrease paranoia a bit, as noticed by Chris Wilson
Reviewed-by: NRodrigo Vivi <rodrigo.vivi@gmail.com>
Reviewed-by: NJesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: NEugeni Dodonov <eugeni.dodonov@intel.com>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_display.c

@@ -1299,6 +1299,69 @@ static void intel_disable_pll(struct drm_i915_private *dev_priv, enum pipe pipe)
 	POSTING_READ(reg);
 }
 
+/* SBI access */
+static void
+intel_sbi_write(struct drm_i915_private *dev_priv, u16 reg, u32 value)
+{
+	unsigned long flags;
+
+	spin_lock_irqsave(&dev_priv->dpio_lock, flags);
+	if (wait_for((I915_READ(SBI_CTL_STAT) & SBI_READY) == 0,
+				100)) {
+		DRM_ERROR("timeout waiting for SBI to become ready\n");
+		goto out_unlock;
+	}
+
+	I915_WRITE(SBI_ADDR,
+			(reg << 16));
+	I915_WRITE(SBI_DATA,
+			value);
+	I915_WRITE(SBI_CTL_STAT,
+			SBI_BUSY |
+			SBI_CTL_OP_CRWR);
+
+	if (wait_for((I915_READ(SBI_CTL_STAT) & (SBI_READY | SBI_RESPONSE_SUCCESS)) == 0,
+				100)) {
+		DRM_ERROR("timeout waiting for SBI to complete write transaction\n");
+		goto out_unlock;
+	}
+
+out_unlock:
+	spin_unlock_irqrestore(&dev_priv->dpio_lock, flags);
+}
+
+static u32
+intel_sbi_read(struct drm_i915_private *dev_priv, u16 reg)
+{
+	unsigned long flags;
+	u32 value;
+
+	spin_lock_irqsave(&dev_priv->dpio_lock, flags);
+	if (wait_for((I915_READ(SBI_CTL_STAT) & SBI_READY) == 0,
+				100)) {
+		DRM_ERROR("timeout waiting for SBI to become ready\n");
+		goto out_unlock;
+	}
+
+	I915_WRITE(SBI_ADDR,
+			(reg << 16));
+	I915_WRITE(SBI_CTL_STAT,
+			SBI_BUSY |
+			SBI_CTL_OP_CRRD);
+
+	if (wait_for((I915_READ(SBI_CTL_STAT) & (SBI_READY | SBI_RESPONSE_SUCCESS)) == 0,
+				100)) {
+		DRM_ERROR("timeout waiting for SBI to complete read transaction\n");
+		goto out_unlock;
+	}
+
+	value = I915_READ(SBI_DATA);
+
+out_unlock:
+	spin_unlock_irqrestore(&dev_priv->dpio_lock, flags);
+	return value;
+}
+
 /**
  * intel_enable_pch_pll - enable PCH PLL
  * @dev_priv: i915 private structure