drm/i915/gen6+: Interpret mailbox error flags

In order to add proper support for the SAGV, we need to be able to know
what the cause of a failure to change the SAGV through the pcode mailbox
was. The reasoning for this is that some very early pre-release Skylake
machines don't actually allow you to control the SAGV on them, and
indicate an invalid mailbox command was sent.

This also might come in handy in the future for debugging.

Changes since v1:
 - Add functions for interpreting gen6 mailbox error codes along with
   gen7+ error codes, and actually interpret those codes properly
 - Renamed patch to reflect new behavior
Signed-off-by: Lyude <cpaul@redhat.com>
Cc: Matt Roper <matthew.d.roper@intel.com>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: stable@vger.kernel.org
Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1471463761-26796-2-git-send-email-cpaul@redhat.com
[mlankhorst: -ENOSYS -> -ENXIO for checkpatch]

drivers/gpu/drm/i915/i915_reg.h

@@ -7123,6 +7123,15 @@ enum {
 
 #define GEN6_PCODE_MAILBOX			_MMIO(0x138124)
 #define   GEN6_PCODE_READY			(1<<31)
+#define   GEN6_PCODE_ERROR_MASK			0xFF
+#define     GEN6_PCODE_SUCCESS			0x0
+#define     GEN6_PCODE_ILLEGAL_CMD		0x1
+#define     GEN6_PCODE_MIN_FREQ_TABLE_GT_RATIO_OUT_OF_RANGE 0x2
+#define     GEN6_PCODE_TIMEOUT			0x3
+#define     GEN6_PCODE_UNIMPLEMENTED_CMD	0xFF
+#define     GEN7_PCODE_TIMEOUT			0x2
+#define     GEN7_PCODE_ILLEGAL_DATA		0x3
+#define     GEN7_PCODE_MIN_FREQ_TABLE_GT_RATIO_OUT_OF_RANGE 0x10
 #define	  GEN6_PCODE_WRITE_RC6VIDS		0x4
 #define	  GEN6_PCODE_READ_RC6VIDS		0x5
 #define     GEN6_ENCODE_RC6_VID(mv)		(((mv) - 245) / 5)

drivers/gpu/drm/i915/intel_pm.c

@@ -7659,8 +7659,53 @@ void intel_init_pm(struct drm_device *dev)
 	}
 }
 
+static inline int gen6_check_mailbox_status(struct drm_i915_private *dev_priv)
+{
+	uint32_t flags =
+		I915_READ_FW(GEN6_PCODE_MAILBOX) & GEN6_PCODE_ERROR_MASK;
+
+	switch (flags) {
+	case GEN6_PCODE_SUCCESS:
+		return 0;
+	case GEN6_PCODE_UNIMPLEMENTED_CMD:
+	case GEN6_PCODE_ILLEGAL_CMD:
+		return -ENXIO;
+	case GEN6_PCODE_MIN_FREQ_TABLE_GT_RATIO_OUT_OF_RANGE:
+		return -EOVERFLOW;
+	case GEN6_PCODE_TIMEOUT:
+		return -ETIMEDOUT;
+	default:
+		MISSING_CASE(flags)
+		return 0;
+	}
+}
+
+static inline int gen7_check_mailbox_status(struct drm_i915_private *dev_priv)
+{
+	uint32_t flags =
+		I915_READ_FW(GEN6_PCODE_MAILBOX) & GEN6_PCODE_ERROR_MASK;
+
+	switch (flags) {
+	case GEN6_PCODE_SUCCESS:
+		return 0;
+	case GEN6_PCODE_ILLEGAL_CMD:
+		return -ENXIO;
+	case GEN7_PCODE_TIMEOUT:
+		return -ETIMEDOUT;
+	case GEN7_PCODE_ILLEGAL_DATA:
+		return -EINVAL;
+	case GEN7_PCODE_MIN_FREQ_TABLE_GT_RATIO_OUT_OF_RANGE:
+		return -EOVERFLOW;
+	default:
+		MISSING_CASE(flags);
+		return 0;
+	}
+}
+
 int sandybridge_pcode_read(struct drm_i915_private *dev_priv, u32 mbox, u32 *val)
 {
+	int status;
+
 	WARN_ON(!mutex_is_locked(&dev_priv->rps.hw_lock));
 
 	/* GEN6_PCODE_* are outside of the forcewake domain, we can
@@ -7687,12 +7732,25 @@ int sandybridge_pcode_read(struct drm_i915_private *dev_priv, u32 mbox, u32 *val
 	*val = I915_READ_FW(GEN6_PCODE_DATA);
 	I915_WRITE_FW(GEN6_PCODE_DATA, 0);
 
+	if (INTEL_GEN(dev_priv) > 6)
+		status = gen7_check_mailbox_status(dev_priv);
+	else
+		status = gen6_check_mailbox_status(dev_priv);
+
+	if (status) {
+		DRM_DEBUG_DRIVER("warning: pcode (read) mailbox access failed: %d\n",
+				 status);
+		return status;
+	}
+
 	return 0;
 }
 
 int sandybridge_pcode_write(struct drm_i915_private *dev_priv,
 			    u32 mbox, u32 val)
 {
+	int status;
+
 	WARN_ON(!mutex_is_locked(&dev_priv->rps.hw_lock));
 
 	/* GEN6_PCODE_* are outside of the forcewake domain, we can
@@ -7717,6 +7775,17 @@ int sandybridge_pcode_write(struct drm_i915_private *dev_priv,
 
 	I915_WRITE_FW(GEN6_PCODE_DATA, 0);
 
+	if (INTEL_GEN(dev_priv) > 6)
+		status = gen7_check_mailbox_status(dev_priv);
+	else
+		status = gen6_check_mailbox_status(dev_priv);
+
+	if (status) {
+		DRM_DEBUG_DRIVER("warning: pcode (write) mailbox access failed: %d\n",
+				 status);
+		return status;
+	}
+
 	return 0;
 }