linux-kernel - Re: [PATCH v1 7/9] drm/bridge: tc358768: fix TXTAGOCNT computation

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Date:   Fri, 5 May 2023 20:03:44 +0200
From:   Robert Foss <rfoss@...nel.org>
To:     Francesco Dolcini <francesco@...cini.it>
Cc:     Andrzej Hajda <andrzej.hajda@...el.com>,
        Neil Armstrong <neil.armstrong@...aro.org>,
        Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
        Jonas Karlman <jonas@...boo.se>,
        Jernej Skrabec <jernej.skrabec@...il.com>,
        tomi.valkeinen@...asonboard.com, dri-devel@...ts.freedesktop.org,
        Francesco Dolcini <francesco.dolcini@...adex.com>,
        David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 7/9] drm/bridge: tc358768: fix TXTAGOCNT computation

On Thu, Apr 27, 2023 at 4:35 PM Francesco Dolcini <francesco@...cini.it> wrote:
>
> From: Francesco Dolcini <francesco.dolcini@...adex.com>
>
> Correct computation of TXTAGOCNT register.
>
> This register must be set to a value that ensure that the
> TTA-GO period = (4 x TLPX)
>
> with the actual value of TTA-GO being
>
> 4 x (TXTAGOCNT + 1) x (HSByteClk cycle)
>
> Fixes: ff1ca6397b1d ("drm/bridge: Add tc358768 driver")
> Signed-off-by: Francesco Dolcini <francesco.dolcini@...adex.com>
> ---
>  drivers/gpu/drm/bridge/tc358768.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/bridge/tc358768.c b/drivers/gpu/drm/bridge/tc358768.c
> index 36e33cba59a2..854fc04f08d0 100644
> --- a/drivers/gpu/drm/bridge/tc358768.c
> +++ b/drivers/gpu/drm/bridge/tc358768.c
> @@ -795,7 +795,7 @@ static void tc358768_bridge_pre_enable(struct drm_bridge *bridge)
>
>         /* TXTAGOCNT[26:16] RXTASURECNT[10:0] */
>         val = tc358768_to_ns((lptxcnt + 1) * dsibclk_nsk * 4);
> -       val = tc358768_ns_to_cnt(val, dsibclk_nsk) - 1;
> +       val = tc358768_ns_to_cnt(val, dsibclk_nsk) / 4 - 1;
>         val2 = tc358768_ns_to_cnt(tc358768_to_ns((lptxcnt + 1) * dsibclk_nsk),
>                                   dsibclk_nsk) - 2;
>         val = val << 16 | val2;
> --
> 2.25.1
>

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