drm/i915/tgl: Gen12 csb support

The CSB format has been reworked for Gen12 to include information on
both the context we're switching away from and the context we're
switching to. After the change, some of the events don't have their
own bit anymore and need to be inferred from other values in the csb.
One of the context IDs (0x7FF) has also been reserved to indicate
the invalid ctx, i.e. engine idle.

Note that the full context ID includes the SW counter as well, but since
we currently only care if the context is valid or not we can ignore that
part.

v2: fix mask size, fix and expand comments (Tvrtko),
    use if-ladder (Chris)

Bspec: 45555, 46144
Signed-off-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Acked-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20190820102201.29849-1-chris@chris-wilson.co.uk

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

@@ -166,6 +166,13 @@
 
 #define CTX_DESC_FORCE_RESTORE BIT_ULL(2)
 
+#define GEN12_CTX_STATUS_SWITCHED_TO_NEW_QUEUE	(0x1) /* lower csb dword */
+#define GEN12_CTX_SWITCH_DETAIL(csb_dw)	((csb_dw) & 0xF) /* upper csb dword */
+#define GEN12_CSB_SW_CTX_ID_MASK		GENMASK(25, 15)
+#define GEN12_IDLE_CTX_ID		0x7FF
+#define GEN12_CSB_CTX_VALID(csb_dw) \
+	(FIELD_GET(GEN12_CSB_SW_CTX_ID_MASK, csb_dw) != GEN12_IDLE_CTX_ID)
+
 /* Typical size of the average request (2 pipecontrols and a MI_BB) */
 #define EXECLISTS_REQUEST_SIZE 64 /* bytes */
 #define WA_TAIL_DWORDS 2
@@ -1371,8 +1378,71 @@ enum csb_step {
 	CSB_COMPLETE,
 };
 
+/*
+ * Starting with Gen12, the status has a new format:
+ *
+ *     bit  0:     switched to new queue
+ *     bit  1:     reserved
+ *     bit  2:     semaphore wait mode (poll or signal), only valid when
+ *                 switch detail is set to "wait on semaphore"
+ *     bits 3-5:   engine class
+ *     bits 6-11:  engine instance
+ *     bits 12-14: reserved
+ *     bits 15-25: sw context id of the lrc the GT switched to
+ *     bits 26-31: sw counter of the lrc the GT switched to
+ *     bits 32-35: context switch detail
+ *                  - 0: ctx complete
+ *                  - 1: wait on sync flip
+ *                  - 2: wait on vblank
+ *                  - 3: wait on scanline
+ *                  - 4: wait on semaphore
+ *                  - 5: context preempted (not on SEMAPHORE_WAIT or
+ *                       WAIT_FOR_EVENT)
+ *     bit  36:    reserved
+ *     bits 37-43: wait detail (for switch detail 1 to 4)
+ *     bits 44-46: reserved
+ *     bits 47-57: sw context id of the lrc the GT switched away from
+ *     bits 58-63: sw counter of the lrc the GT switched away from
+ */
 static inline enum csb_step
-csb_parse(const struct intel_engine_execlists *execlists, const u32 *csb)
+gen12_csb_parse(const struct intel_engine_execlists *execlists, const u32 *csb)
+{
+	u32 lower_dw = csb[0];
+	u32 upper_dw = csb[1];
+	bool ctx_to_valid = GEN12_CSB_CTX_VALID(lower_dw);
+	bool ctx_away_valid = GEN12_CSB_CTX_VALID(upper_dw);
+	bool new_queue = lower_dw & GEN12_CTX_STATUS_SWITCHED_TO_NEW_QUEUE;
+
+	if (!ctx_away_valid && ctx_to_valid)
+		return CSB_PROMOTE;
+
+	/*
+	 * The context switch detail is not guaranteed to be 5 when a preemption
+	 * occurs, so we can't just check for that. The check below works for
+	 * all the cases we care about, including preemptions of WAIT
+	 * instructions and lite-restore. Preempt-to-idle via the CTRL register
+	 * would require some extra handling, but we don't support that.
+	 */
+	if (new_queue && ctx_away_valid)
+		return CSB_PREEMPT;
+
+	/*
+	 * switch detail = 5 is covered by the case above and we do not expect a
+	 * context switch on an unsuccessful wait instruction since we always
+	 * use polling mode.
+	 */
+	GEM_BUG_ON(GEN12_CTX_SWITCH_DETAIL(upper_dw));
+
+	if (*execlists->active) {
+		GEM_BUG_ON(!ctx_away_valid);
+		return CSB_COMPLETE;
+	}
+
+	return CSB_NOP;
+}
+
+static inline enum csb_step
+gen8_csb_parse(const struct intel_engine_execlists *execlists, const u32 *csb)
 {
 	unsigned int status = *csb;
 
@@ -1424,6 +1494,8 @@ static void process_csb(struct intel_engine_cs *engine)
 	rmb();
 
 	do {
+		enum csb_step csb_step;
+
 		if (++head == num_entries)
 			head = 0;
 
@@ -1449,7 +1521,12 @@ static void process_csb(struct intel_engine_cs *engine)
 			  engine->name, head,
 			  buf[2 * head + 0], buf[2 * head + 1]);
 
-		switch (csb_parse(execlists, buf + 2 * head)) {
+		if (INTEL_GEN(engine->i915) >= 12)
+			csb_step = gen12_csb_parse(execlists, buf + 2 * head);
+		else
+			csb_step = gen8_csb_parse(execlists, buf + 2 * head);
+
+		switch (csb_step) {
 		case CSB_PREEMPT: /* cancel old inflight, prepare for switch */
 			trace_ports(execlists, "preempted", execlists->active);