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References: <20230427142934.55435-1-francesco@dolcini.it> <20230427142934.55435-5-francesco@dolcini.it>
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From:   Robert Foss <rfoss@kernel.org>
Date:   Fri, 5 May 2023 19:41:04 +0200
Message-ID: <CAN6tsi4NmNbQ3dava=rr-Jx4tV37QD6=ujNq2bXDuSaoP8mdrQ@mail.gmail.com>
Subject: Re: [PATCH v1 4/9] drm/bridge: tc358768: fix TCLK_ZEROCNT 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>,
        linux-kernel@vger.kernel.org
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On Thu, Apr 27, 2023 at 4:35=E2=80=AFPM Francesco Dolcini <francesco@dolcin=
i.it> wrote:
>
> From: Francesco Dolcini <francesco.dolcini@toradex.com>
>
> 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>
> ---
>  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/t=
c358768.c
> index dba1bf3912f1..aff400c36066 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_b=
ridge *bridge)
>
>         /* 38ns < TCLK_PREPARE < 95ns */
>         val =3D tc358768_ns_to_cnt(65, dsibclk_nsk) - 1;
> -       /* TCLK_PREPARE > 300ns */
> -       val2 =3D tc358768_ns_to_cnt(300 + tc358768_to_ns(3 * ui_nsk),
> -                                 dsibclk_nsk);
> -       val |=3D (val2 - tc358768_to_ns(phy_delay_nsk - dsibclk_nsk)) << =
8;
> +       /* TCLK_PREPARE + TCLK_ZERO > 300ns */
> +       val2 =3D tc358768_ns_to_cnt(300 - tc358768_to_ns(2 * ui_nsk),
> +                                 dsibclk_nsk) - 2;
> +       val |=3D val2 << 8;
>         dev_dbg(priv->dev, "TCLK_HEADERCNT: 0x%x\n", val);
>         tc358768_write(priv, TC358768_TCLK_HEADERCNT, val);
>
> --
> 2.25.1
>

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