drm/xe/hmm: Style- and include fixes

Add proper #ifndef around the xe_hmm.h header, proper spacing
and since the documentation mostly follows kerneldoc format,
make it kerneldoc. Also prepare for upcoming -stable fixes.

Fixes: 81e058a3e7 ("drm/xe: Introduce helper to populate userptr")
Cc: Oak Zeng <oak.zeng@intel.com>
Cc: <stable@vger.kernel.org> # v6.10+
Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Acked-by: Matthew Brost <Matthew Brost <matthew.brost@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20250304173342.22009-2-thomas.hellstrom@linux.intel.com

drivers/gpu/drm/xe/xe_hmm.c

@@ -19,11 +19,10 @@ static u64 xe_npages_in_range(unsigned long start, unsigned long end)
 	return (end - start) >> PAGE_SHIFT;
 }
 
-/*
+/**
  * xe_mark_range_accessed() - mark a range is accessed, so core mm
  * have such information for memory eviction or write back to
  * hard disk
- *
  * @range: the range to mark
  * @write: if write to this range, we mark pages in this range
  * as dirty
@@ -43,11 +42,10 @@ static void xe_mark_range_accessed(struct hmm_range *range, bool write)
 	}
 }
 
-/*
+/**
  * xe_build_sg() - build a scatter gather table for all the physical pages/pfn
  * in a hmm_range. dma-map pages if necessary. dma-address is save in sg table
  * and will be used to program GPU page table later.
- *
  * @xe: the xe device who will access the dma-address in sg table
  * @range: the hmm range that we build the sg table from. range->hmm_pfns[]
  * has the pfn numbers of pages that back up this hmm address range.
@@ -112,9 +110,8 @@ static int xe_build_sg(struct xe_device *xe, struct hmm_range *range,
 	return ret;
 }
 
-/*
+/**
  * xe_hmm_userptr_free_sg() - Free the scatter gather table of userptr
- *
  * @uvma: the userptr vma which hold the scatter gather table
  *
  * With function xe_userptr_populate_range, we allocate storage of

drivers/gpu/drm/xe/xe_hmm.h

@@ -3,9 +3,14 @@
  * Copyright © 2024 Intel Corporation
  */
 
+#ifndef _XE_HMM_H_
+#define _XE_HMM_H_
+
 #include <linux/types.h>
 
 struct xe_userptr_vma;
 
 int xe_hmm_userptr_populate_range(struct xe_userptr_vma *uvma, bool is_mm_mmap_locked);
+
 void xe_hmm_userptr_free_sg(struct xe_userptr_vma *uvma);
+#endif