drm/i915/gt: Explicitly clear BB_OFFSET for new contexts

Even though the initial protocontext we load onto HW has the register
cleared, by the time we save it into the default image, BB_OFFSET has
had the enable bit set. Reclear BB_OFFSET for each new context.

Testcase: igt/i915_selftests/gt_lrc

v2:
  Extend it for gen8.
v3:
  BB_OFFSET is recorded per engine from Gen9 onwards
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Signed-off-by: Ramalingam C <ramalingam.c@intel.com>
Reviewed-by: Thomas Hellstrom <thomas.hellstrom@linux.intel.com>
Signed-off-by: Karolina Drobnik <karolina.drobnik@intel.com>
Reviewed-by: Andi Shyti <andi.shyti@linux.intel.com>
Signed-off-by: Andi Shyti <andi.shyti@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/37c67abb3303852f06a570a4360addf52bf941c1.1663081418.git.karolina.drobnik@intel.com

drivers/gpu/drm/i915/gt/intel_engine_regs.h

@@ -110,6 +110,7 @@
 #define RING_SBBSTATE(base)			_MMIO((base) + 0x118) /* hsw+ */
 #define RING_SBBADDR_UDW(base)			_MMIO((base) + 0x11c) /* gen8+ */
 #define RING_BBADDR(base)			_MMIO((base) + 0x140)
+#define RING_BB_OFFSET(base)			_MMIO((base) + 0x158)
 #define RING_BBADDR_UDW(base)			_MMIO((base) + 0x168) /* gen8+ */
 #define CCID(base)				_MMIO((base) + 0x180)
 #define   CCID_EN				BIT(0)

drivers/gpu/drm/i915/gt/intel_lrc.c

@@ -662,6 +662,21 @@ static int lrc_ring_mi_mode(const struct intel_engine_cs *engine)
 		return -1;
 }
 
+static int lrc_ring_bb_offset(const struct intel_engine_cs *engine)
+{
+	if (GRAPHICS_VER_FULL(engine->i915) >= IP_VER(12, 50))
+		return 0x80;
+	else if (GRAPHICS_VER(engine->i915) >= 12)
+		return 0x70;
+	else if (GRAPHICS_VER(engine->i915) >= 9)
+		return 0x64;
+	else if (GRAPHICS_VER(engine->i915) >= 8 &&
+		 engine->class == RENDER_CLASS)
+		return 0xc4;
+	else
+		return -1;
+}
+
 static int lrc_ring_gpr0(const struct intel_engine_cs *engine)
 {
 	if (GRAPHICS_VER_FULL(engine->i915) >= IP_VER(12, 50))
@@ -768,6 +783,7 @@ static void init_common_regs(u32 * const regs,
 			     bool inhibit)
 {
 	u32 ctl;
+	int loc;
 
 	ctl = _MASKED_BIT_ENABLE(CTX_CTRL_INHIBIT_SYN_CTX_SWITCH);
 	ctl |= _MASKED_BIT_DISABLE(CTX_CTRL_ENGINE_CTX_RESTORE_INHIBIT);
@@ -779,6 +795,10 @@ static void init_common_regs(u32 * const regs,
 	regs[CTX_CONTEXT_CONTROL] = ctl;
 
 	regs[CTX_TIMESTAMP] = ce->stats.runtime.last;
+
+	loc = lrc_ring_bb_offset(engine);
+	if (loc != -1)
+		regs[loc + 1] = 0;
 }
 
 static void init_wa_bb_regs(u32 * const regs,

drivers/gpu/drm/i915/gt/selftest_lrc.c

@@ -357,6 +357,11 @@ static int live_lrc_fixed(void *arg)
 				lrc_ring_cmd_buf_cctl(engine),
 				"RING_CMD_BUF_CCTL"
 			},
+			{
+				i915_mmio_reg_offset(RING_BB_OFFSET(engine->mmio_base)),
+				lrc_ring_bb_offset(engine),
+				"RING_BB_OFFSET"
+			},
 			{ },
 		}, *t;
 		u32 *hw;