drm/cma-helper: Release non-coherent memory with dma_free_noncoherent()

The GEM CMA helpers allocate non-coherent (i.e., cached) backing storage
with dma_alloc_noncoherent(), but release it with dma_free_wc(). Fix this
with a call to dma_free_noncoherent(). Writecombining storage is still
released with dma_free_wc().

Signed-off-by: Thomas Zimmermann <[e-mail]>
Fixes: cf8ccbc72d61 ("drm: Add support for GEM buffers backed by non-coherent memory")
Acked-by: Paul Cercueil <[e-mail]>
Cc: Thomas Zimmermann <[e-mail]>
Cc: Maarten Lankhorst <[e-mail]>
Cc: Maxime Ripard <[e-mail]>
Cc: David Airlie <[e-mail]>
Cc: Daniel Vetter <[e-mail]>
Cc: [e-mail]
Cc: <[e-mail]> # v5.14+
Link: https://patchwork.freedesktop.org/patch/msgid/[e-mail]

drivers/gpu/drm/drm_gem_cma_helper.c

···
 			dma_buf_vunmap(gem_obj->import_attach->dmabuf, &map);
 		drm_prime_gem_destroy(gem_obj, cma_obj->sgt);
 	} else if (cma_obj->vaddr) {
-		dma_free_wc(gem_obj->dev->dev, cma_obj->base.size,
-			    cma_obj->vaddr, cma_obj->paddr);
+		if (cma_obj->map_noncoherent)
+			dma_free_noncoherent(gem_obj->dev->dev, cma_obj->base.size,
+					     cma_obj->vaddr, cma_obj->paddr,
+					     DMA_TO_DEVICE);
+		else
+			dma_free_wc(gem_obj->dev->dev, cma_obj->base.size,
+				    cma_obj->vaddr, cma_obj->paddr);
 	}
 
 	drm_gem_object_release(gem_obj);