drm/xe: Implement xe_pagefault_init

Create pagefault queues and initialize them.

v2:
 - Fix kernel doc + add comment for number PF queue (Francois)
v4:
 - Move init after GT init (CI, Francois)

Signed-off-by: Matthew Brost <matthew.brost@intel.com>
Reviewed-by: Francois Dugast <francois.dugast@intel.com>
Tested-by: Francois Dugast <francois.dugast@intel.com>
Link: https://patch.msgid.link/20251031165416.2871503-3-matthew.brost@intel.com

drivers/gpu/drm/xe/xe_device.c

@@ -52,6 +52,7 @@
 #include "xe_nvm.h"
 #include "xe_oa.h"
 #include "xe_observation.h"
+#include "xe_pagefault.h"
 #include "xe_pat.h"
 #include "xe_pcode.h"
 #include "xe_pm.h"
@@ -896,6 +897,10 @@ int xe_device_probe(struct xe_device *xe)
 			return err;
 	}
 
+	err = xe_pagefault_init(xe);
+	if (err)
+		return err;
+
 	if (xe->tiles->media_gt &&
 	    XE_GT_WA(xe->tiles->media_gt, 15015404425_disable))
 		XE_DEVICE_WA_DISABLE(xe, 15015404425);

drivers/gpu/drm/xe/xe_device_types.h

@@ -18,6 +18,7 @@
 #include "xe_lmtt_types.h"
 #include "xe_memirq_types.h"
 #include "xe_oa_types.h"
+#include "xe_pagefault_types.h"
 #include "xe_platform_types.h"
 #include "xe_pmu_types.h"
 #include "xe_pt_types.h"
@@ -413,6 +414,16 @@ struct xe_device {
 		u32 next_asid;
 		/** @usm.lock: protects UM state */
 		struct rw_semaphore lock;
+		/** @usm.pf_wq: page fault work queue, unbound, high priority */
+		struct workqueue_struct *pf_wq;
+		/*
+		 * We pick 4 here because, in the current implementation, it
+		 * yields the best bandwidth utilization of the kernel paging
+		 * engine.
+		 */
+#define XE_PAGEFAULT_QUEUE_COUNT	4
+		/** @usm.pf_queue: Page fault queues */
+		struct xe_pagefault_queue pf_queue[XE_PAGEFAULT_QUEUE_COUNT];
 	} usm;
 
 	/** @pinned: pinned BO state */

drivers/gpu/drm/xe/xe_pagefault.c

@@ -3,6 +3,10 @@
  * Copyright © 2025 Intel Corporation
  */
 
+#include <drm/drm_managed.h>
+
+#include "xe_device.h"
+#include "xe_gt_types.h"
 #include "xe_pagefault.h"
 #include "xe_pagefault_types.h"
 
@@ -21,6 +25,76 @@
  * xe_pagefault.c implements the consumer layer.
  */
 
+static int xe_pagefault_entry_size(void)
+{
+	/*
+	 * Power of two alignment is not a hardware requirement, rather a
+	 * software restriction which makes the math for page fault queue
+	 * management simplier.
+	 */
+	return roundup_pow_of_two(sizeof(struct xe_pagefault));
+}
+
+static void xe_pagefault_queue_work(struct work_struct *w)
+{
+	/* TODO: Implement */
+}
+
+static int xe_pagefault_queue_init(struct xe_device *xe,
+				   struct xe_pagefault_queue *pf_queue)
+{
+	struct xe_gt *gt;
+	int total_num_eus = 0;
+	u8 id;
+
+	for_each_gt(gt, xe, id) {
+		xe_dss_mask_t all_dss;
+		int num_dss, num_eus;
+
+		bitmap_or(all_dss, gt->fuse_topo.g_dss_mask,
+			  gt->fuse_topo.c_dss_mask, XE_MAX_DSS_FUSE_BITS);
+
+		num_dss = bitmap_weight(all_dss, XE_MAX_DSS_FUSE_BITS);
+		num_eus = bitmap_weight(gt->fuse_topo.eu_mask_per_dss,
+					XE_MAX_EU_FUSE_BITS) * num_dss;
+
+		total_num_eus += num_eus;
+	}
+
+	xe_assert(xe, total_num_eus);
+
+	/*
+	 * user can issue separate page faults per EU and per CS
+	 *
+	 * XXX: Multiplier required as compute UMD are getting PF queue errors
+	 * without it. Follow on why this multiplier is required.
+	 */
+#define PF_MULTIPLIER	8
+	pf_queue->size = (total_num_eus + XE_NUM_HW_ENGINES) *
+		xe_pagefault_entry_size() * PF_MULTIPLIER;
+	pf_queue->size = roundup_pow_of_two(pf_queue->size);
+#undef PF_MULTIPLIER
+
+	drm_dbg(&xe->drm, "xe_pagefault_entry_size=%d, total_num_eus=%d, pf_queue->size=%u",
+		xe_pagefault_entry_size(), total_num_eus, pf_queue->size);
+
+	spin_lock_init(&pf_queue->lock);
+	INIT_WORK(&pf_queue->worker, xe_pagefault_queue_work);
+
+	pf_queue->data = drmm_kzalloc(&xe->drm, pf_queue->size, GFP_KERNEL);
+	if (!pf_queue->data)
+		return -ENOMEM;
+
+	return 0;
+}
+
+static void xe_pagefault_fini(void *arg)
+{
+	struct xe_device *xe = arg;
+
+	destroy_workqueue(xe->usm.pf_wq);
+}
+
 /**
  * xe_pagefault_init() - Page fault init
  * @xe: xe device instance
@@ -31,8 +105,28 @@
  */
 int xe_pagefault_init(struct xe_device *xe)
 {
-	/* TODO - implement */
-	return 0;
+	int err, i;
+
+	if (!xe->info.has_usm)
+		return 0;
+
+	xe->usm.pf_wq = alloc_workqueue("xe_page_fault_work_queue",
+					WQ_UNBOUND | WQ_HIGHPRI,
+					XE_PAGEFAULT_QUEUE_COUNT);
+	if (!xe->usm.pf_wq)
+		return -ENOMEM;
+
+	for (i = 0; i < XE_PAGEFAULT_QUEUE_COUNT; ++i) {
+		err = xe_pagefault_queue_init(xe, xe->usm.pf_queue + i);
+		if (err)
+			goto err_out;
+	}
+
+	return devm_add_action_or_reset(xe->drm.dev, xe_pagefault_fini, xe);
+
+err_out:
+	destroy_workqueue(xe->usm.pf_wq);
+	return err;
 }
 
 /**