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

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Message-ID: <CA+V-a8vjjY94KX-oWY5gKqNsWRvmxs2gzc1hDFjqCxbg+Y8c4g@mail.gmail.com>
Date: Wed, 21 May 2025 14:06:28 +0100
From: "Lad, Prabhakar" <prabhakar.csengg@...il.com>
To: Geert Uytterhoeven <geert@...ux-m68k.org>
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 Geert,

Thank you for the review.

On Tue, May 20, 2025 at 3:55 PM Geert Uytterhoeven <geert@...ux-m68k.org> wrote:
>
> 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/
>
Agreed, I will update it to use KILO (and below).

Cheers,
Prabhakar

> > +
> >         /*
> >          * 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