drm: apple: Align PIODMA buffers to SZ_16K

The iommu scatter table/list mapping can only map full iommu page size
extents. Just align the actual the allocation to the iommu page size.
This could be handled differently using DARTs subpage protection but
there's no easy way to integrate that.

Signed-off-by: Janne Grunau <j@jannau.net>

drivers/gpu/drm/apple/iomfb_template.c

@@ -279,7 +279,10 @@ static struct dcp_map_buf_resp dcpep_cb_map_piodma(struct apple_dcp *dcp,
 	ret = iommu_map_sgtable(dcp->iommu_dom, memdesc->dva, map,
 				IOMMU_READ | IOMMU_WRITE);
 
-	if (ret != memdesc->size) {
+	/* HACK: expect size to be 16K aligned since the iommu API only maps
+	 *       full pages
+	 */
+	if (ret < 0 || ret != ALIGN(memdesc->size, SZ_16K)) {
 		dev_err(dcp->dev, "iommu_map_sgtable() returned %zd instead of expected buffer size of %zu\n", ret, memdesc->size);
 		goto reject;
 	}
@@ -334,6 +337,7 @@ dcpep_cb_allocate_buffer(struct apple_dcp *dcp,
 {
 	struct dcp_allocate_buffer_resp resp = { 0 };
 	struct dcp_mem_descriptor *memdesc;
+	size_t size;
 	u32 id;
 
 	resp.dva_size = ALIGN(req->size, 4096);
@@ -352,11 +356,13 @@ dcpep_cb_allocate_buffer(struct apple_dcp *dcp,
 	memdesc = &dcp->memdesc[id];
 
 	memdesc->size = resp.dva_size;
-	memdesc->buf = dma_alloc_coherent(dcp->dev, memdesc->size,
+	/* HACK: align size to 16K since the iommu API only maps full pages */
+	size = ALIGN(resp.dva_size, SZ_16K);
+	memdesc->buf = dma_alloc_coherent(dcp->dev, size,
 					  &memdesc->dva, GFP_KERNEL);
 
 	dma_get_sgtable(dcp->dev, &memdesc->map, memdesc->buf, memdesc->dva,
-			memdesc->size);
+			size);
 	resp.dva = memdesc->dva;
 
 	return resp;