[PATCH 6.4 238/800] drm/bridge: tc358768: fix TCLK_ZEROCNT computation

Greg Kroah-Hartman
2023-07-16T20:04:00Z

From: Francesco Dolcini <francesco.dolcini@toradex.com>

[ Upstream commit f9cf811374f42fca31ac34aaf59ee2ae72b89879 ]

Correct computation of TCLK_ZEROCNT register.

This register must be set to a value that ensure that
(TCLK-PREPARECNT + TCLK-ZERO) > 300ns

with the actual value of (TCLK-PREPARECNT + TCLK-ZERO) being

(1 to 2) + (TCLK_ZEROCNT + 1)) x HSByteClkCycle + (PHY output delay)

with PHY output delay being about

(2 to 3) x MIPIBitClk cycle in the BitClk conversion.

Fixes: ff1ca6397b1d ("drm/bridge: Add tc358768 driver")
Signed-off-by: Francesco Dolcini <francesco.dolcini@toradex.com>
Reviewed-by: Robert Foss <rfoss@kernel.org>
Signed-off-by: Robert Foss <rfoss@kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20230427142934.55435-5-francesco@dolcini.it
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/gpu/drm/bridge/tc358768.c | 8 ++++----
1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/bridge/tc358768.c b/drivers/gpu/drm/bridge/tc358768.c
index dba1bf3912f1e..aff400c360662 100644
--- a/drivers/gpu/drm/bridge/tc358768.c
+++ b/drivers/gpu/drm/bridge/tc358768.c
@@ -742,10 +742,10 @@ static void tc358768_bridge_pre_enable(struct drm_bridge *bridge)

/* 38ns < TCLK_PREPARE < 95ns */
val = tc358768_ns_to_cnt(65, dsibclk_nsk) - 1;
- /* TCLK_PREPARE > 300ns */
- val2 = tc358768_ns_to_cnt(300 + tc358768_to_ns(3 * ui_nsk),
- dsibclk_nsk);
- val |= (val2 - tc358768_to_ns(phy_delay_nsk - dsibclk_nsk)) << 8;
+ /* TCLK_PREPARE + TCLK_ZERO > 300ns */
+ val2 = tc358768_ns_to_cnt(300 - tc358768_to_ns(2 * ui_nsk),
+ dsibclk_nsk) - 2;
+ val |= val2 << 8;
dev_dbg(priv->dev, "TCLK_HEADERCNT: 0x%x\n", val);
tc358768_write(priv, TC358768_TCLK_HEADERCNT, val);

--
2.39.2