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References: <20230427142934.55435-1-francesco@dolcini.it> <20230427142934.55435-9-francesco@dolcini.it>
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From:   Robert Foss <rfoss@kernel.org>
Date:   Fri, 5 May 2023 20:06:59 +0200
Message-ID: <CAN6tsi54HRw6STzkxbChxdCK+oV+8EF0taO6dSp8YpsokQ8TCQ@mail.gmail.com>
Subject: Re: [PATCH v1 8/9] drm/bridge: tc358768: fix THS_TRAILCNT computation
To:     Francesco Dolcini <francesco@dolcini.it>
Cc:     Andrzej Hajda <andrzej.hajda@intel.com>,
        Neil Armstrong <neil.armstrong@linaro.org>,
        Laurent Pinchart <Laurent.pinchart@ideasonboard.com>,
        Jonas Karlman <jonas@kwiboo.se>,
        Jernej Skrabec <jernej.skrabec@gmail.com>,
        tomi.valkeinen@ideasonboard.com, dri-devel@lists.freedesktop.org,
        Francesco Dolcini <francesco.dolcini@toradex.com>,
        David Airlie <airlied@gmail.com>,
        Daniel Vetter <daniel@ffwll.ch>, linux-kernel@vger.kernel.org
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On Thu, Apr 27, 2023 at 4:34=E2=80=AFPM Francesco Dolcini <francesco@dolcin=
i.it> wrote:
>
> From: Francesco Dolcini <francesco.dolcini@toradex.com>
>
> 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 =3D 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: ff1ca6397b1d ("drm/bridge: Add tc358768 driver")
> Signed-off-by: Francesco Dolcini <francesco.dolcini@toradex.com>
> ---
>  drivers/gpu/drm/bridge/tc358768.c | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/gpu/drm/bridge/tc358768.c b/drivers/gpu/drm/bridge/t=
c358768.c
> index 854fc04f08d0..947c7dca567a 100644
> --- a/drivers/gpu/drm/bridge/tc358768.c
> +++ b/drivers/gpu/drm/bridge/tc358768.c
> @@ -779,9 +779,10 @@ static void tc358768_bridge_pre_enable(struct drm_br=
idge *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 =3D 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 =3D tc358768_ns_to_cnt(60 + tc358768_to_ns(18 * ui_nsk),
> +                                    dsibclk_nsk) - 4;
> +       val =3D clamp(raw_val, 0, 15);
>         dev_dbg(priv->dev, "THS_TRAILCNT: 0x%x\n", val);
>         tc358768_write(priv, TC358768_THS_TRAILCNT, val);
>
> --
> 2.25.1
>

Reviewed-by: Robert Foss <rfoss@kernel.org>