linux-kernel - [PATCH 2/7] drm/vc4: Fix DSI T

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Message-Id: <20170615204130.19255-3-eric@anholt.net>
Date:   Thu, 15 Jun 2017 13:41:25 -0700
From:   Eric Anholt <eric@...olt.net>
To:     dri-devel@...ts.freedesktop.org,
        Archit Taneja <architt@...eaurora.org>,
        Andrzej Hajda <a.hajda@...sung.com>,
        Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
        Thierry Reding <thierry.reding@...il.com>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>, devicetree@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, Eric Anholt <eric@...olt.net>
Subject: [PATCH 2/7] drm/vc4: Fix DSI T_INIT timing.

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@...olt.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 5e8b81eaa168..15f6d5005ab9 100644
--- a/drivers/gpu/drm/vc4/vc4_dsi.c
+++ b/drivers/gpu/drm/vc4/vc4_dsi.c
@@ -1035,7 +1035,17 @@ 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