linux-kernel - Re: [PATCH v8 2/6] clk: renesas: rzv2h-cpg: Add support for DSI clocks

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Message-ID: <CAMuHMdUacF5UfiLTXuWOXAZZvEJ-St5+awkWML_HDp9b38=sXw@mail.gmail.com>
Date: Wed, 24 Sep 2025 15:05:18 +0200
From: Geert Uytterhoeven <geert@...ux-m68k.org>
To: Prabhakar <prabhakar.csengg@...il.com>
Cc: Andrzej Hajda <andrzej.hajda@...el.com>, Neil Armstrong <neil.armstrong@...aro.org>, 
	Robert Foss <rfoss@...nel.org>, Laurent Pinchart <Laurent.pinchart@...asonboard.com>, 
	Tomi Valkeinen <tomi.valkeinen+renesas@...asonboard.com>, Jonas Karlman <jonas@...boo.se>, 
	Jernej Skrabec <jernej.skrabec@...il.com>, 
	Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, Maxime Ripard <mripard@...nel.org>, 
	Thomas Zimmermann <tzimmermann@...e.de>, David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>, 
	Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley <conor+dt@...nel.org>, 
	Michael Turquette <mturquette@...libre.com>, Stephen Boyd <sboyd@...nel.org>, 
	Biju Das <biju.das.jz@...renesas.com>, Magnus Damm <magnus.damm@...il.com>, 
	dri-devel@...ts.freedesktop.org, devicetree@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-renesas-soc@...r.kernel.org, 
	linux-clk@...r.kernel.org, Fabrizio Castro <fabrizio.castro.jz@...esas.com>, 
	Tommaso Merciai <tommaso.merciai.xr@...renesas.com>, 
	Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>
Subject: Re: [PATCH v8 2/6] clk: renesas: rzv2h-cpg: Add support for DSI clocks

Hi Prabhakar,

On Wed, 3 Sept 2025 at 18:17, Prabhakar <prabhakar.csengg@...il.com> wrote:
> From: Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>
>
> Add support for PLLDSI and PLLDSI divider clocks.
>
> Introduce the `renesas-rzv2h-cpg-pll.h` header to centralize and share
> PLLDSI related data structures, limits, and algorithms between the
> RZ/V2H(P) CPG and DSI drivers.
>
> The DSI PLL is functionally similar to the CPG's PLLDSI, but has slightly
> different parameter limits and omits the programmable divider present in
> CPG. To ensure precise frequency calculations, especially for milliHz-level
> accuracy needed by the DSI driver, the shared algorithm allows both drivers
> to compute PLL parameters consistently using the same logic and input
> clock.
>
> Co-developed-by: Fabrizio Castro <fabrizio.castro.jz@...esas.com>
> Signed-off-by: Fabrizio Castro <fabrizio.castro.jz@...esas.com>
> Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>
> Reviewed-by: Biju Das <biju.das.jz@...renesas.com>
> Reviewed-by: Geert Uytterhoeven <geert+renesas@...der.be>

> --- a/drivers/clk/renesas/rzv2h-cpg.c
> +++ b/drivers/clk/renesas/rzv2h-cpg.c

> +static int rzv2h_cpg_plldsi_div_determine_rate(struct clk_hw *hw,
> +                                              struct clk_rate_request *req)
> +{
> +       struct rzv2h_plldsi_div_clk *dsi_div = to_plldsi_div_clk(hw);
> +       struct pll_clk *pll_clk = to_pll(clk_hw_get_parent(hw));
> +       struct rzv2h_cpg_priv *priv = dsi_div->priv;
> +       struct rzv2h_pll_div_pars *dsi_params;
> +       struct rzv2h_pll_dsi_info *dsi_info;
> +       u64 rate_millihz;
> +
> +       dsi_info = &priv->pll_dsi_info[pll_clk->pll.instance];
> +       dsi_params = &dsi_info->pll_dsi_parameters;
> +
> +       rate_millihz = mul_u32_u32(req->rate, MILLI);
> +       if (rate_millihz == dsi_params->div.error_millihz + dsi_params->div.freq_millihz)
> +               goto exit_determine_rate;
> +
> +       if (!rzv2h_get_pll_dtable_pars(dsi_info->pll_dsi_limits, dsi_params, dsi_div->dtable,
> +                                      rate_millihz)) {
> +               dev_err(priv->dev,
> +                       "failed to determine rate for req->rate: %lu\n",
> +                       req->rate);
> +               return -EINVAL;
> +       }
> +
> +exit_determine_rate:
> +       req->rate = DIV_ROUND_CLOSEST_ULL(dsi_params->div.freq_millihz, MILLI);
> +       req->best_parent_rate = req->rate * dsi_params->div.divider_value;
> +       dsi_info->req_pll_dsi_rate = req->best_parent_rate;
> +
> +       return 0;
> +};

Unneeded semicolon (there are three more below).

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds