From: Thierry Reding <tred...@nvidia.com>

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 <tred...@nvidia.com>
---
 drivers/gpu/drm/tegra/plane.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/drivers/gpu/drm/tegra/plane.c b/drivers/gpu/drm/tegra/plane.c
index 19e8847a164b..793da5d675d2 100644
--- 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
-- 
2.30.2

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