[PATCH v4 3/8] drm/xe/debugfs: add page-size allocation mode knob

[Nareshkumar Gollakoti <naresh.kumar.g@intel.com>]

Expose a debugfs control to override the page-size allocation mode used
for user BOs.

The interface allows switching between the default allocation policy,
forced 2M, forced 1G, and mixed allocation modes at runtime. This
provides a simple way to validate behavior and debug page-size-dependent
allocation flows.

The debugfs entry is built only when CONFIG_DRM_XE_DEBUG_PAGE_SIZE is
enabled.

v2
- update changelog to match mutex-based cur_index handling
- reset cur_index when switching to mixed mode (sashiko)

v3
- add CONFIG guard for page-size allocation debugfs support (Himal)
- create debugfs entry under CONFIG_DRM_XE_DEBUG_PAGE_SIZE

v4
- reorderd this patch with kconfig patch to ensure patch builds
- Gurding this debug knob for only discrete graphics

Signed-off-by: Nareshkumar Gollakoti <naresh.kumar.g@intel.com>
---
 drivers/gpu/drm/xe/xe_debugfs.c | 62 +++++++++++++++++++++++++++++++++
 1 file changed, 62 insertions(+)

diff --git a/drivers/gpu/drm/xe/xe_debugfs.c b/drivers/gpu/drm/xe/xe_debugfs.c
index 8c391c7b017a..6ab2d51033f8 100644
--- a/drivers/gpu/drm/xe/xe_debugfs.c
+++ b/drivers/gpu/drm/xe/xe_debugfs.c
@@ -564,6 +564,56 @@ static const struct file_operations disable_late_binding_fops = {
 	.write = disable_late_binding_set,
 };
 
+#if IS_ENABLED(CONFIG_DRM_XE_DEBUG_PAGE_SIZE)
+static ssize_t page_size_alloc_mode_show(struct file *f, char __user *ubuf,
+					 size_t size, loff_t *pos)
+{
+	struct xe_device *xe = file_inode(f)->i_private;
+	char buf[32];
+	int len;
+
+	mutex_lock(&xe->page_size_alloc_ctrl.lock);
+
+	len = scnprintf(buf, sizeof(buf), "%u\n",
+			xe->page_size_alloc_ctrl.mode);
+	mutex_unlock(&xe->page_size_alloc_ctrl.lock);
+
+	return simple_read_from_buffer(ubuf, size, pos, buf, len);
+}
+
+static ssize_t page_size_alloc_mode_set(struct file *f, const char __user *ubuf,
+					size_t size, loff_t *pos)
+{
+	struct xe_device *xe = file_inode(f)->i_private;
+	unsigned int val;
+	int ret;
+
+	ret = kstrtouint_from_user(ubuf, size, 0, &val);
+	if (ret)
+		return ret;
+
+	if (val > XE_PAGE_SIZE_ALLOC_CTRL_MODE_MIXED)
+		return -EINVAL;
+
+	mutex_lock(&xe->page_size_alloc_ctrl.lock);
+
+	if (val == XE_PAGE_SIZE_ALLOC_CTRL_MODE_MIXED)
+		xe->page_size_alloc_ctrl.cur_index = 0;
+
+	xe->page_size_alloc_ctrl.mode = (enum xe_page_size_alloc_ctrl_mode)val;
+
+	mutex_unlock(&xe->page_size_alloc_ctrl.lock);
+
+	return size;
+}
+
+static const struct file_operations page_size_alloc_mode_fops = {
+	.owner = THIS_MODULE,
+	.read = page_size_alloc_mode_show,
+	.write = page_size_alloc_mode_set,
+};
+#endif
+
 void xe_debugfs_register(struct xe_device *xe)
 {
 	struct ttm_device *bdev = &xe->ttm;
@@ -616,6 +666,18 @@ void xe_debugfs_register(struct xe_device *xe)
 
 	debugfs_create_file("disable_late_binding", 0600, root, xe,
 			    &disable_late_binding_fops);
+#if IS_ENABLED(CONFIG_DRM_XE_DEBUG_PAGE_SIZE)
+	/*
+	 * Expose a debugfs knob to control user BO page-size allocation:
+	 * 0 - default behavior
+	 * 1 - force 2M page allocations
+	 * 2 - force 1G page allocations
+	 * 3 - mixed mode: select 4K, 64K, 2M, and 1G in round-robin order
+	 */
+	if (IS_DGFX(xe))
+		debugfs_create_file("page_size_alloc_mode", 0600, root, xe,
+				    &page_size_alloc_mode_fops);
+#endif
 
 	/*
 	 * Don't expose page reclaim configuration file if not supported by the
-- 
2.43.0