linux-kernel - Re: [PATCH v1 2/9] drm/bridge: tc358768: fix PLL parameters computation

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Date:   Fri, 5 May 2023 19:36:23 +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 2/9] drm/bridge: tc358768: fix PLL parameters computation

On Thu, Apr 27, 2023 at 4:35 PM Francesco Dolcini <francesco@...cini.it> wrote:
>
> From: Francesco Dolcini <francesco.dolcini@...adex.com>
>
> According to Toshiba documentation the PLL input clock after the divider
> should be not less than 4MHz, fix the PLL parameters computation
> accordingly.
>
> Fixes: ff1ca6397b1d ("drm/bridge: Add tc358768 driver")
> Signed-off-by: Francesco Dolcini <francesco.dolcini@...adex.com>
> ---
>  drivers/gpu/drm/bridge/tc358768.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/bridge/tc358768.c b/drivers/gpu/drm/bridge/tc358768.c
> index 8f349bf4fc32..e9e3f9e02bba 100644
> --- a/drivers/gpu/drm/bridge/tc358768.c
> +++ b/drivers/gpu/drm/bridge/tc358768.c
> @@ -334,13 +334,17 @@ static int tc358768_calc_pll(struct tc358768_priv *priv,
>                 u32 fbd;
>
>                 for (fbd = 0; fbd < 512; ++fbd) {
> -                       u32 pll, diff;
> +                       u32 pll, diff, pll_in;
>
>                         pll = (u32)div_u64((u64)refclk * (fbd + 1), divisor);
>
>                         if (pll >= max_pll || pll < min_pll)
>                                 continue;
>
> +                       pll_in = (u32)div_u64((u64)refclk, prd + 1);
> +                       if (pll_in < 4000000)
> +                               continue;
> +
>                         diff = max(pll, target_pll) - min(pll, target_pll);
>
>                         if (diff < best_diff) {
> --
> 2.25.1
>

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