[PATCH v4 07/12] drm/xe/pat: Return error from xe_pat_init_early() on unknown platform

[Dnyaneshwar Bhadane <dnyaneshwar.bhadane@intel.com>]

xe_pat_init_early() currently only logs an error when the platform's
graphics version doesn't match any known PAT table, but continues
probing with an uninitialized pat.ops. This can lead to a NULL
pointer dereference later when pat.ops is used.

Change xe_pat_init_early() to return an int and propagate -ENODATA
to xe_device_probe() so the driver fails to load cleanly instead of
continuing in a broken state.

Fixes: 152d7f2db978 ("drm/xe/pat: Handle unicast vs MCR PAT registers")
Signed-off-by: Dnyaneshwar Bhadane <dnyaneshwar.bhadane@intel.com>
---
v2:
 - Update kernel-doc for xe_pat_init_early. (Michal)
---
---
 drivers/gpu/drm/xe/xe_device.c |  4 +++-
 drivers/gpu/drm/xe/xe_pat.c    | 13 ++++++++++++-
 drivers/gpu/drm/xe/xe_pat.h    |  4 +++-
 3 files changed, 18 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/xe/xe_device.c b/drivers/gpu/drm/xe/xe_device.c
index 44975e7823be..327f018fe15e 100644
--- a/drivers/gpu/drm/xe/xe_device.c
+++ b/drivers/gpu/drm/xe/xe_device.c
@@ -879,7 +879,9 @@ int xe_device_probe(struct xe_device *xe)
 	int err;
 	u8 id;
 
-	xe_pat_init_early(xe);
+	err = xe_pat_init_early(xe);
+	if (err)
+		return err;
 
 	err = xe_sriov_init(xe);
 	if (err)
diff --git a/drivers/gpu/drm/xe/xe_pat.c b/drivers/gpu/drm/xe/xe_pat.c
index a5fe1beec652..519f7d5a2765 100644
--- a/drivers/gpu/drm/xe/xe_pat.c
+++ b/drivers/gpu/drm/xe/xe_pat.c
@@ -590,7 +590,13 @@ static const struct xe_pat_ops xe3p_xpc_pat_ops = {
 	.entry_dump = xe3p_xpc_pat_entry_dump,
 };
 
-void xe_pat_init_early(struct xe_device *xe)
+/**
+ * xe_pat_init_early() - Init early pat table operation.
+ * @xe: the &xe_device
+ *
+ * Return: 0 on success or a negative error code on failure.
+ */
+int xe_pat_init_early(struct xe_device *xe)
 {
 	xe->pat.idx[XE_CACHE_WB_COMPRESSION] = XE_PAT_INVALID_IDX;
 	xe->pat.idx[XE_CACHE_NONE_COMPRESSION] = XE_PAT_INVALID_IDX;
@@ -686,14 +692,19 @@ void xe_pat_init_early(struct xe_device *xe)
 		 * raise an error rather than trying to silently inherit the
 		 * most recent platform's behavior.
 		 */
+
 		drm_err(&xe->drm, "Missing PAT table for platform with graphics version %d.%02d!\n",
 			GRAPHICS_VER(xe), GRAPHICS_VERx100(xe) % 100);
+		return -ENODATA;
+
 	}
 
+	xe_assert(xe, xe->pat.ops);
 	xe_assert(xe, xe->pat.ops->dump);
 	xe_assert(xe, xe->pat.ops->program_graphics);
 	xe_assert(xe, MEDIA_VER(xe) < 13 || xe->pat.ops->program_media);
 	xe_assert(xe, GRAPHICS_VER(xe) < 20 || xe->pat.ops->entry_dump);
+	return 0;
 }
 
 void xe_pat_init(struct xe_gt *gt)
diff --git a/drivers/gpu/drm/xe/xe_pat.h b/drivers/gpu/drm/xe/xe_pat.h
index 7060f66e1d63..6398c3ab4805 100644
--- a/drivers/gpu/drm/xe/xe_pat.h
+++ b/drivers/gpu/drm/xe/xe_pat.h
@@ -42,8 +42,10 @@ struct xe_pat_table_entry {
 /**
  * xe_pat_init_early - SW initialization, setting up data based on device
  * @xe: xe device
+ *
+ * Return: 0 on success or a negative error code on failure.
  */
-void xe_pat_init_early(struct xe_device *xe);
+int xe_pat_init_early(struct xe_device *xe);
 
 /**
  * xe_pat_init - Program HW PAT table
-- 
2.54.0