linux-kernel - Re: [PATCH v5 05/12] drm: renesas: rz-du: mipi

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Message-ID: <CAMuHMdVEgTo7V-gzzpVVNqxnDMSdTC1ew70gbJ=Sb5Qr4asryA@mail.gmail.com>
Date: Tue, 20 May 2025 16:54:57 +0200
From: Geert Uytterhoeven <geert@...ux-m68k.org>
To: Prabhakar <prabhakar.csengg@...il.com>
Cc: Biju Das <biju.das.jz@...renesas.com>, David Airlie <airlied@...il.com>, 
	Simona Vetter <simona@...ll.ch>, Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, 
	Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>, Rob Herring <robh@...nel.org>, 
	Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley <conor+dt@...nel.org>, 
	Philipp Zabel <p.zabel@...gutronix.de>, Magnus Damm <magnus.damm@...il.com>, 
	Laurent Pinchart <laurent.pinchart+renesas@...asonboard.com>, dri-devel@...ts.freedesktop.org, 
	linux-renesas-soc@...r.kernel.org, devicetree@...r.kernel.org, 
	linux-kernel@...r.kernel.org, 
	Fabrizio Castro <fabrizio.castro.jz@...esas.com>, 
	Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>
Subject: Re: [PATCH v5 05/12] drm: renesas: rz-du: mipi_dsi: Use VCLK for
 HSFREQ calculation

Hi Prabhakar,

On Mon, 12 May 2025 at 20:23, Prabhakar <prabhakar.csengg@...il.com> wrote:
> From: Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>
>
> Update the RZ/G2L MIPI DSI driver to calculate HSFREQ using the actual
> VCLK rate instead of the mode clock. The relationship between HSCLK and
> VCLK is:
>
>     vclk * bpp <= hsclk * 8 * lanes
>
> Retrieve the VCLK rate using `clk_get_rate(dsi->vclk)`, ensuring that
> HSFREQ accurately reflects the clock rate set in hardware, leading to
> better precision in data transmission.
>
> Additionally, use `DIV_ROUND_CLOSEST_ULL` for a more precise division
> when computing `hsfreq`. Also, update unit conversions to use correct
> scaling factors for better clarity and correctness.
>
> Since `clk_get_rate()` returns the clock rate in Hz, update the HSFREQ
> threshold comparisons to use Hz instead of kHz to ensure correct behavior.
>
> 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>
> ---
> v4->v5:
> - Added dev_info() to print the VCLK rate if it doesn't match the
>   requested rate.
> - Added Reviewed-by tag from Biju
>
> v3->v4:
> - Used MILLI instead of KILO

Thanks for the update!

> --- a/drivers/gpu/drm/renesas/rz-du/rzg2l_mipi_dsi.c
> +++ b/drivers/gpu/drm/renesas/rz-du/rzg2l_mipi_dsi.c

> @@ -269,6 +271,12 @@ static int rzg2l_mipi_dsi_startup(struct rzg2l_mipi_dsi *dsi,
>         u32 golpbkt;
>         int ret;
>
> +       ret = pm_runtime_resume_and_get(dsi->dev);
> +       if (ret < 0)
> +               return ret;
> +
> +       clk_set_rate(dsi->vclk, mode->clock * MILLI);

drm_display_mode.clock is in kHz, so s/MILLI/KILO/

> +
>         /*
>          * Relationship between hsclk and vclk must follow
>          * vclk * bpp = hsclk * 8 * lanes
> @@ -280,13 +288,11 @@ static int rzg2l_mipi_dsi_startup(struct rzg2l_mipi_dsi *dsi,
>          * hsclk(bit) = hsclk(byte) * 8 = hsfreq
>          */
>         bpp = mipi_dsi_pixel_format_to_bpp(dsi->format);
> -       hsfreq = (mode->clock * bpp) / dsi->lanes;
> -
> -       ret = pm_runtime_resume_and_get(dsi->dev);
> -       if (ret < 0)
> -               return ret;
> -
> -       clk_set_rate(dsi->vclk, mode->clock * 1000);
> +       vclk_rate = clk_get_rate(dsi->vclk);
> +       if (vclk_rate != mode->clock * MILLI)
> +               dev_info(dsi->dev, "Requested vclk rate %lu, actual %lu mismatch\n",
> +                        mode->clock * MILLI, vclk_rate);

Likewise.

> +       hsfreq = DIV_ROUND_CLOSEST_ULL(vclk_rate * bpp, dsi->lanes);
>
>         ret = rzg2l_mipi_dsi_dphy_init(dsi, hsfreq);
>         if (ret < 0)

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