Re: [PATCH v1 6/9] drm/bridge: tc358768: fix THS_ZEROCNT computation

[Robert Foss]

On Thu, Apr 27, 2023 at 4:33 PM Francesco Dolcini <francesco@xxxxxxxxxx> wrote:
>
> From: Francesco Dolcini <francesco.dolcini@xxxxxxxxxxx>
>
> Correct computation of THS_ZEROCNT register.
>
> This register must be set to a value that ensure that
> THS_PREPARE + THS_ZERO > 145ns + 10*UI
>
> with the actual value of (THS_PREPARE + THS_ZERO) being
>
> ((1 to 2) + 1 + (TCLK_ZEROCNT + 1) + (3 to 4)) x ByteClk cycle +
>   + HSByteClk x (2 + (1 to 2)) + (PHY delay)
>
> with PHY 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@xxxxxxxxxxx>
> ---
>  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/tc358768.c
> index 360c7c65f8c4..36e33cba59a2 100644
> --- a/drivers/gpu/drm/bridge/tc358768.c
> +++ b/drivers/gpu/drm/bridge/tc358768.c
> @@ -760,9 +760,10 @@ static void tc358768_bridge_pre_enable(struct drm_bridge *bridge)
>         /* 40ns + 4*UI < THS_PREPARE < 85ns + 6*UI */
>         val = 50 + tc358768_to_ns(4 * ui_nsk);
>         val = tc358768_ns_to_cnt(val, dsibclk_nsk) - 1;
> -       /* THS_ZERO > 145ns + 10*UI */
> -       val2 = tc358768_ns_to_cnt(145 - tc358768_to_ns(ui_nsk), dsibclk_nsk);
> -       val |= (val2 - tc358768_to_ns(phy_delay_nsk)) << 8;
> +       /* THS_PREPARE + THS_ZERO > 145ns + 10*UI */
> +       raw_val = tc358768_ns_to_cnt(145 - tc358768_to_ns(3 * ui_nsk), dsibclk_nsk) - 10;
> +       val2 = clamp(raw_val, 0, 127);
> +       val |= val2 << 8;
>         dev_dbg(priv->dev, "THS_HEADERCNT: 0x%x\n", val);
>         tc358768_write(priv, TC358768_THS_HEADERCNT, val);
>
> --
> 2.25.1
>

Reviewed-by: Robert Foss <rfoss@xxxxxxxxxx>