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drm/bridge: tc358768: fix THS_TRAILCNT computation

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[ Upstream commit bac7842cd179572e8e0fc2d7b5254e40c6e9e057 ]

Correct computation of THS_TRAILCNT register.

This register must be set to a value that ensure that
THS_TRAIL > 60 ns + 4 x UI
 and
THS_TRAIL > 8 x UI
 and
THS_TRAIL < TEOT
 with
TEOT = 105 ns + (12 x UI)

with the actual value of THS_TRAIL being

(1 + THS_TRAILCNT) x ByteClk cycle + ((1 to 2) + 2) xHSBYTECLK cycle +
 - (PHY output delay)

with PHY output delay being about

(8 + (5 to 6)) x MIPIBitClk cycle in the BitClk conversion.

Fixes: ff1ca6397b ("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/20230427142934.55435-9-francesco@dolcini.it
Signed-off-by: Sasha Levin <sashal@kernel.org>
This commit is contained in:
Francesco Dolcini 2023-04-27 16:29:33 +02:00 committed by Greg Kroah-Hartman
parent f2f7d0a4a2
commit 46a34e1459
1 changed files with 4 additions and 3 deletions
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7
drivers/gpu/drm/bridge/tc358768.c
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@ -763,9 +763,10 @@ static void tc358768_bridge_pre_enable(struct drm_bridge *bridge)
dev_dbg(priv->dev, "TCLK_POSTCNT: 0x%x\n", val);
tc358768_write(priv, TC358768_TCLK_POSTCNT, val);
/* 60ns + 4*UI < THS_PREPARE < 105ns + 12*UI */
val = tc358768_ns_to_cnt(60 + tc358768_to_ns(15 * ui_nsk),
dsibclk_nsk) - 5;
/* max(60ns + 4*UI, 8*UI) < THS_TRAILCNT < 105ns + 12*UI */
raw_val = tc358768_ns_to_cnt(60 + tc358768_to_ns(18 * ui_nsk),
dsibclk_nsk) - 4;
val = clamp(raw_val, 0, 15);
dev_dbg(priv->dev, "THS_TRAILCNT: 0x%x\n", val);
tc358768_write(priv, TC358768_THS_TRAILCNT, val);