drm/tegra: gem: Add a clarifying comment

Clarify when a fixed IOV address can be used and when a buffer has to
be mapped before the IOVA can be used.

Signed-off-by: Thierry Reding <treding@nvidia.com>

diff --git a/drivers/gpu/drm/tegra/plane.c b/drivers/gpu/drm/tegra/plane.c
index 19e8847..793da5d 100644 (file)
--- a/drivers/gpu/drm/tegra/plane.c
+++ b/drivers/gpu/drm/tegra/plane.c
@@ -119,6 +119,14 @@ static int tegra_dc_pin(struct tegra_dc *dc, struct tegra_plane_state *state)
                dma_addr_t phys_addr, *phys;
                struct sg_table *sgt;
 
+               /*
+                * If we're not attached to a domain, we already stored the
+                * physical address when the buffer was allocated. If we're
+                * part of a group that's shared between all display
+                * controllers, we've also already mapped the framebuffer
+                * through the SMMU. In both cases we can short-circuit the
+                * code below and retrieve the stored IOV address.
+                */
                if (!domain || dc->client.group)
                        phys = &phys_addr;
                else