[PATCH v5 05/12] drm: renesas: rz-du: mipi_dsi: Use VCLK for HSFREQ calculation

[Lad, Prabhakar]

Hi Laurent,

Thank you for the review.

On Tue, May 20, 2025 at 3:16 PM Laurent Pinchart
<laurent.pinchart at ideasonboard.com> wrote:
>
> Hi Prabhakar,
>
> On Mon, May 12, 2025 at 07:23:23PM +0100, Prabhakar wrote:
> > From: Lad Prabhakar <prabhakar.mahadev-lad.rj at bp.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 at renesas.com>
> > Signed-off-by: Fabrizio Castro <fabrizio.castro.jz at renesas.com>
> > Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj at bp.renesas.com>
> > Reviewed-by: Biju Das <biju.das.jz at bp.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
> >
> > v2->v3:
> > - No changes
> >
> > v1->v2:
> > - No changes
> > ---
> >  .../gpu/drm/renesas/rz-du/rzg2l_mipi_dsi.c    | 30 +++++++++++--------
> >  1 file changed, 18 insertions(+), 12 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/renesas/rz-du/rzg2l_mipi_dsi.c b/drivers/gpu/drm/renesas/rz-du/rzg2l_mipi_dsi.c
> > index c5f698cd74f1..3f6988303e63 100644
> > --- a/drivers/gpu/drm/renesas/rz-du/rzg2l_mipi_dsi.c
> > +++ b/drivers/gpu/drm/renesas/rz-du/rzg2l_mipi_dsi.c
> > @@ -8,6 +8,7 @@
> >  #include <linux/delay.h>
> >  #include <linux/io.h>
> >  #include <linux/iopoll.h>
> > +#include <linux/math.h>
> >  #include <linux/module.h>
> >  #include <linux/of.h>
> >  #include <linux/of_graph.h>
> > @@ -15,6 +16,7 @@
> >  #include <linux/pm_runtime.h>
> >  #include <linux/reset.h>
> >  #include <linux/slab.h>
> > +#include <linux/units.h>
> >
> >  #include <drm/drm_atomic.h>
> >  #include <drm/drm_atomic_helper.h>
> > @@ -199,7 +201,7 @@ static int rzg2l_mipi_dsi_dphy_init(struct rzg2l_mipi_dsi *dsi,
> >       /* All DSI global operation timings are set with recommended setting */
> >       for (i = 0; i < ARRAY_SIZE(rzg2l_mipi_dsi_global_timings); ++i) {
> >               dphy_timings = &rzg2l_mipi_dsi_global_timings[i];
> > -             if (hsfreq <= dphy_timings->hsfreq_max)
> > +             if (hsfreq <= (dphy_timings->hsfreq_max * MILLI))
>
> No need for the inner parentheses.
>
Agreed, I will drop it.

> >                       break;
> >       }
> >
> > @@ -258,7 +260,7 @@ static void rzg2l_mipi_dsi_dphy_exit(struct rzg2l_mipi_dsi *dsi)
> >  static int rzg2l_mipi_dsi_startup(struct rzg2l_mipi_dsi *dsi,
> >                                 const struct drm_display_mode *mode)
> >  {
> > -     unsigned long hsfreq;
> > +     unsigned long hsfreq, vclk_rate;
> >       unsigned int bpp;
> >       u32 txsetr;
> >       u32 clstptsetr;
> > @@ -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);
> > +
> >       /*
> >        * 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);
>
> There's a high risk that the requested rate won't be achieved exactly.
> Do we really want to print a non-debug message to the kernel log every
> time ?
>
Actually Biju requested the above.

> > +     hsfreq = DIV_ROUND_CLOSEST_ULL(vclk_rate * bpp, dsi->lanes);
>
> I doubt DIV_ROUND_CLOSEST_ULL() will make any difference in practice
> given that you can't have more than 4 lanes, but that's fine.
>
Thanks, I'll check on it.

Cheers,
Prabhakar
> >
> >       ret = rzg2l_mipi_dsi_dphy_init(dsi, hsfreq);
> >       if (ret < 0)
> > @@ -304,12 +310,12 @@ static int rzg2l_mipi_dsi_startup(struct rzg2l_mipi_dsi *dsi,
> >        * - data lanes: maximum 4 lanes
> >        * Therefore maximum hsclk will be 891 Mbps.
> >        */
> > -     if (hsfreq > 445500) {
> > +     if (hsfreq > 445500000) {
> >               clkkpt = 12;
> >               clkbfht = 15;
> >               clkstpt = 48;
> >               golpbkt = 75;
> > -     } else if (hsfreq > 250000) {
> > +     } else if (hsfreq > 250000000) {
> >               clkkpt = 7;
> >               clkbfht = 8;
> >               clkstpt = 27;
> > @@ -753,7 +759,7 @@ static int rzg2l_mipi_dsi_probe(struct platform_device *pdev)
> >        * mode->clock and format are not available. So initialize DPHY with
> >        * timing parameters for 80Mbps.
> >        */
> > -     ret = rzg2l_mipi_dsi_dphy_init(dsi, 80000);
> > +     ret = rzg2l_mipi_dsi_dphy_init(dsi, 80000000);
> >       if (ret < 0)
> >               goto err_phy;
> >
>
> --
> Regards,
>
> Laurent Pinchart