[PATCH v11 1/7] drm/i915/gen6+: Return -EINVAL on invalid pcode commands

[Lyude <cpaul@redhat.com>]

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.

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
---
 drivers/gpu/drm/i915/i915_reg.h |  1 +
 drivers/gpu/drm/i915/intel_pm.c | 10 ++++++++++
 2 files changed, 11 insertions(+)

diff --git a/drivers/gpu/drm/i915/i915_reg.h b/drivers/gpu/drm/i915/i915_reg.h
index da82744..73b3d4d 100644
--- a/drivers/gpu/drm/i915/i915_reg.h
+++ b/drivers/gpu/drm/i915/i915_reg.h
@@ -7121,6 +7121,7 @@ enum {
 #define VLV_MEDIA_C0_COUNT			_MMIO(0x13811C)
 
 #define GEN6_PCODE_MAILBOX			_MMIO(0x138124)
+#define   GEN6_PCODE_INVALID_CMD		(1<<0)
 #define   GEN6_PCODE_READY			(1<<31)
 #define	  GEN6_PCODE_WRITE_RC6VIDS		0x4
 #define	  GEN6_PCODE_READ_RC6VIDS		0x5
diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
index 99014d7..8752730 100644
--- a/drivers/gpu/drm/i915/intel_pm.c
+++ b/drivers/gpu/drm/i915/intel_pm.c
@@ -7674,6 +7674,11 @@ 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 (I915_READ_FW(GEN6_PCODE_MAILBOX) & GEN6_PCODE_INVALID_CMD) {
+		DRM_DEBUG_DRIVER("warning: pcode (read) mailbox access indicated invalid command\n");
+		return -EINVAL;
+	}
+
 	return 0;
 }
 
@@ -7704,6 +7709,11 @@ int sandybridge_pcode_write(struct drm_i915_private *dev_priv,
 
 	I915_WRITE_FW(GEN6_PCODE_DATA, 0);
 
+	if (I915_READ_FW(GEN6_PCODE_MAILBOX) & GEN6_PCODE_INVALID_CMD) {
+		DRM_DEBUG_DRIVER("warning: pcode (write) mailbox access indicated invalid command\n");
+		return -EINVAL;
+	}
+
 	return 0;
 }
 
-- 
2.7.4