[PATCH] lib/xe/xe_spin: Add switch point for preemptible spinner

[Jonathan Cavitt]

From: Niranjana Vishwanathapura <niranjana.vishwanathapura at intel.com>

When 'preempt' option is specified, insert a MI_SEMAPHORE_WAIT
command in the spinner batch buffer. This provides the switch
point for preemption to happen in multi queue mode.

Additionally, allow the user to control the preempt wait condition.

Closes: https://gitlab.freedesktop.org/drm/xe/kernel/-/issues/5783
Signed-off-by: Niranjana Vishwanathapura <niranjana.vishwanathapura at intel.com>
Cc: Matthew Brost <matthew.brost at intel.com>
Signed-off-by: Jonathan Cavitt <jonathan.cavitt at intel.com>
---
 include/intel_gpu_commands.h |  1 +
 lib/xe/xe_spin.c             | 42 +++++++++++++++++++++++++++++++++++-
 lib/xe/xe_spin.h             |  3 +++
 3 files changed, 45 insertions(+), 1 deletion(-)

diff --git a/include/intel_gpu_commands.h b/include/intel_gpu_commands.h
index cd281ba89d..5158bb0ea0 100644
--- a/include/intel_gpu_commands.h
+++ b/include/intel_gpu_commands.h
@@ -123,6 +123,7 @@
 #define MI_SEMAPHORE_WAIT	MI_INSTR(0x1c, 2) /* GEN8+ */
 #define MI_SEMAPHORE_WAIT_TOKEN	MI_INSTR(0x1c, 3) /* GEN12+ */
 #define   MI_SEMAPHORE_POLL		(1 << 15)
+#define   MI_SEMAPHORE_QUEUE_SWITCH_MODE	(1 << 11)
 #define   MI_SEMAPHORE_SAD_GT_SDD	(0 << 12)
 #define   MI_SEMAPHORE_SAD_GTE_SDD	(1 << 12)
 #define   MI_SEMAPHORE_SAD_LT_SDD	(2 << 12)
diff --git a/lib/xe/xe_spin.c b/lib/xe/xe_spin.c
index 25f7555e27..d62952b539 100644
--- a/lib/xe/xe_spin.c
+++ b/lib/xe/xe_spin.c
@@ -30,7 +30,6 @@
 
 enum { START_TS, NOW_TS };
 
-
 uint32_t xe_spin_nsec_to_ticks(int fd, int gt_id, uint64_t nsec)
 {
 	uint32_t ticks = xe_nsec_to_ticks(fd, gt_id, nsec);
@@ -57,6 +56,7 @@ void xe_spin_init(struct xe_spin *spin, struct xe_spin_opts *opts)
 
 	spin->start = 0;
 	spin->end = 0xffffffff;
+	spin->wait_cond = 0;
 	spin->ticks_delta = 0;
 
 	if (opts->ctx_ticks) {
@@ -167,6 +167,24 @@ void xe_spin_init(struct xe_spin *spin, struct xe_spin_opts *opts)
 				   opts->mem_copy->dst->mocs_index;
 	}
 
+	/*
+	 * Insert a MI_SEMAPHORE_WAIT_CMD instruction with condition controlled
+	 * by the user. It also acts as a queue switch point in multi queue mode.
+	 */
+	if (opts->preempt) {
+		uint64_t wait_addr = opts->addr + offsetof(struct xe_spin, wait_cond);
+
+		spin->batch[b++] = MI_SEMAPHORE_WAIT_CMD |
+				MI_SEMAPHORE_POLL |
+				MI_SEMAPHORE_QUEUE_SWITCH_MODE |
+				MI_SEMAPHORE_SAD_EQ_SDD |
+				3;
+		spin->batch[b++] = 0;
+		spin->batch[b++] = wait_addr;
+		spin->batch[b++] = wait_addr >> 32;
+		spin->batch[b++] = 0;
+	}
+
 	spin->batch[b++] = MI_COND_BATCH_BUFFER_END | MI_DO_COMPARE | 2;
 	spin->batch[b++] = 0;
 	spin->batch[b++] = end_addr;
@@ -207,6 +225,28 @@ void xe_spin_end(struct xe_spin *spin)
 	WRITE_ONCE(spin->end, 0);
 }
 
+/**
+ * xe_spin_preempt_wait:
+ * @spin: pointer to spinner mapped bo
+ *
+ * Make the spinner wait on the preemption semaphore.
+ */
+void xe_spin_preempt_wait(struct xe_spin *spin)
+{
+	spin->wait_cond = 1;
+}
+
+/**
+ * xe_spin_preempt_nowait:
+ * @spin: pointer to spinner mapped bo
+ *
+ * Make the spinner do not wait on the preemption semaphore.
+ */
+void xe_spin_preempt_nowait(struct xe_spin *spin)
+{
+	spin->wait_cond = 0;
+}
+
 /**
  * xe_spin_create:
  * @opt: controlling options such as allocator handle, exec_queue, vm etc
diff --git a/lib/xe/xe_spin.h b/lib/xe/xe_spin.h
index c2199d0aa2..eaf2a409e0 100644
--- a/lib/xe/xe_spin.h
+++ b/lib/xe/xe_spin.h
@@ -64,6 +64,7 @@ struct xe_spin {
 	uint64_t pad;
 	uint32_t start;
 	uint32_t end;
+	uint32_t wait_cond;
 	uint32_t ticks_delta;
 	uint64_t exec_sync;
 	uint32_t timestamp;
@@ -76,6 +77,8 @@ void xe_spin_init(struct xe_spin *spin, struct xe_spin_opts *opts);
 bool xe_spin_started(struct xe_spin *spin);
 void xe_spin_wait_started(struct xe_spin *spin);
 void xe_spin_end(struct xe_spin *spin);
+void xe_spin_preempt_wait(struct xe_spin *spin);
+void xe_spin_preempt_nowait(struct xe_spin *spin);
 
 /*
  * xe_cork: higher level API that simplifies exec'ing an xe_spin by taking care
-- 
2.43.0