[PATCH 1/2] drm/vc4: Fix DSI T_INIT timing.

[Eric Anholt <eric@anholt.net>]

The DPHY spec requires a much larger T_INIT than I was specifying
before.  In the absence of clear specs from the slave of what their
timing is, just use the value that the firmware was using.

Signed-off-by: Eric Anholt <eric@anholt.net>
---
 drivers/gpu/drm/vc4/vc4_dsi.c | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/vc4/vc4_dsi.c b/drivers/gpu/drm/vc4/vc4_dsi.c
index 160f981d1cf4..3bad8bad32a2 100644
--- a/drivers/gpu/drm/vc4/vc4_dsi.c
+++ b/drivers/gpu/drm/vc4/vc4_dsi.c
@@ -1094,7 +1094,17 @@ static void vc4_dsi_encoder_enable(struct drm_encoder *encoder)
 				     DSI_HS_DLT4_TRAIL) |
 		       VC4_SET_FIELD(0, DSI_HS_DLT4_ANLAT));
 
-	DSI_PORT_WRITE(HS_DLT5, VC4_SET_FIELD(dsi_hs_timing(ui_ns, 1000, 5000),
+	/* T_INIT is how long STOP is driven after power-up to
+	 * indicate to the slave (also coming out of power-up) that
+	 * master init is complete, and should be greater than the
+	 * maximum of two value: T_INIT,MASTER and T_INIT,SLAVE.  The
+	 * D-PHY spec gives a minimum 100us for T_INIT,MASTER and
+	 * T_INIT,SLAVE, while allowing protocols on top of it to give
+	 * greater minimums.  The vc4 firmware uses an extremely
+	 * conservative 5ms, and we maintain that here.
+	 */
+	DSI_PORT_WRITE(HS_DLT5, VC4_SET_FIELD(dsi_hs_timing(ui_ns,
+							    5 * 1000 * 1000, 0),
 					      DSI_HS_DLT5_INIT));
 
 	DSI_PORT_WRITE(HS_DLT6,
-- 
2.11.0