drm/i915/lmem: Fail driver init if LMEM training failed

Boot firmware performs memory training and health assessment during
startup.  If the memory training fails, the firmware will consider the
GPU unusable and will instruct the punit to keep the GT powered down.
If this happens, our driver will be unable to communicate with the GT
(all GT registers will read back as 0, forcewake requests will timeout,
etc.) so we should abort driver initialization if this happens.  We can
confirm that LMEM was initialized successfully via sgunit register
GU_CNTL.

Bspec: 53111
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
Cc: Caz Yokoyama <Caz.Yokoyama@intel.com>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210420131842.164163-5-matthew.auld@intel.com

drivers/gpu/drm/i915/i915_reg.h

@@ -487,6 +487,9 @@ static inline bool i915_mmio_reg_valid(i915_reg_t reg)
 #define GAB_CTL				_MMIO(0x24000)
 #define   GAB_CTL_CONT_AFTER_PAGEFAULT	(1 << 8)
 
+#define GU_CNTL				_MMIO(0x101010)
+#define   LMEM_INIT			REG_BIT(7)
+
 #define GEN6_STOLEN_RESERVED		_MMIO(0x1082C0)
 #define GEN6_STOLEN_RESERVED_ADDR_MASK	(0xFFF << 20)
 #define GEN7_STOLEN_RESERVED_ADDR_MASK	(0x3FFF << 18)

drivers/gpu/drm/i915/intel_uncore.c

@@ -1917,6 +1917,18 @@ int intel_uncore_init_mmio(struct intel_uncore *uncore)
 	if (ret)
 		return ret;
 
+	/*
+	 * The boot firmware initializes local memory and assesses its health.
+	 * If memory training fails, the punit will have been instructed to
+	 * keep the GT powered down; we won't be able to communicate with it
+	 * and we should not continue with driver initialization.
+	 */
+	if (IS_DGFX(i915) &&
+	    !(__raw_uncore_read32(uncore, GU_CNTL) & LMEM_INIT)) {
+		drm_err(&i915->drm, "LMEM not initialized by firmware\n");
+		return -ENODEV;
+	}
+
 	if (INTEL_GEN(i915) > 5 && !intel_vgpu_active(i915))
 		uncore->flags |= UNCORE_HAS_FORCEWAKE;