drm/i915: Add ww context to intel_dpt_pin, v2.

Ensure i915_vma_pin_iomap and vma_unpin are done with dpt->obj lock held.

I don't think there's much of a point in merging intel_dpt_pin() with
intel_pin_fb_obj_dpt(), they touch different objects.

Changes since v1:
- Fix using the wrong pointer to retrieve error code (Julia)
Signed-off-by: NMaarten Lankhorst <maarten.lankhorst@linux.intel.com>
Reported-by: Nkernel test robot <lkp@intel.com>
Reported-by: NJulia Lawall <julia.lawall@lip6.fr>
Reviewed-by: NThomas Hellström <thomas.hellstrom@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210929085950.3063191-1-maarten.lankhorst@linux.intel.com

drivers/gpu/drm/i915/display/intel_dpt.c

@@ -121,32 +121,42 @@ struct i915_vma *intel_dpt_pin(struct i915_address_space *vm)
 	intel_wakeref_t wakeref;
 	struct i915_vma *vma;
 	void __iomem *iomem;
+	struct i915_gem_ww_ctx ww;
+	int err;
 
 	wakeref = intel_runtime_pm_get(&i915->runtime_pm);
 	atomic_inc(&i915->gpu_error.pending_fb_pin);
 
-	vma = i915_gem_object_ggtt_pin(dpt->obj, NULL, 0, 4096,
-				       HAS_LMEM(i915) ? 0 : PIN_MAPPABLE);
-	if (IS_ERR(vma))
-		goto err;
+	for_i915_gem_ww(&ww, err, true) {
+		err = i915_gem_object_lock(dpt->obj, &ww);
+		if (err)
+			continue;
 
-	iomem = i915_vma_pin_iomap(vma);
-	i915_vma_unpin(vma);
-	if (IS_ERR(iomem)) {
-		vma = ERR_CAST(iomem);
-		goto err;
-	}
+		vma = i915_gem_object_ggtt_pin_ww(dpt->obj, &ww, NULL, 0, 4096,
+						  HAS_LMEM(i915) ? 0 : PIN_MAPPABLE);
+		if (IS_ERR(vma)) {
+			err = PTR_ERR(vma);
+			continue;
+		}
+
+		iomem = i915_vma_pin_iomap(vma);
+		i915_vma_unpin(vma);
 
-	dpt->vma = vma;
-	dpt->iomem = iomem;
+		if (IS_ERR(iomem)) {
+			err = PTR_ERR(iomem);
+			continue;
+		}
 
-	i915_vma_get(vma);
+		dpt->vma = vma;
+		dpt->iomem = iomem;
+
+		i915_vma_get(vma);
+	}
 
-err:
 	atomic_dec(&i915->gpu_error.pending_fb_pin);
 	intel_runtime_pm_put(&i915->runtime_pm, wakeref);
 
-	return vma;
+	return err ? ERR_PTR(err) : vma;
 }
 
 void intel_dpt_unpin(struct i915_address_space *vm)