Re: [PATCH v6 11/22] clk: sunxi-ng: a64: Add minimum rate for PLL_MIPI

[Maxime Ripard]

On Thu, Jul 11, 2019 at 07:43:16PM +0200, Michael Nazzareno Trimarchi wrote:
> > > tcon-pixel clock is the rate that you want to achive on display side
> > > and if you have 4 lanes 32bit or lanes and different bit number that
> > > you need to have a clock that is able to put outside bits and speed
> > > equal to pixel-clock * bits / lanes. so If you want a pixel-clock of
> > > 40 mhz and you have 32bits and 4 lanes you need to have a clock of
> > > 40 * 32 / 4 in no-burst mode. I think that this is done but most of
> > > the display.
> >
> > So this is what the issue is then?
> >
> > This one does make sense, and you should just change the rate in the
> > call to clk_set_rate in sun4i_tcon0_mode_set_cpu.
> >
> > I'm still wondering why that hasn't been brought up in either the
> > discussion or the commit log before though.
> >
> Something like this?
>
> drivers/gpu/drm/sun4i/sun4i_tcon.c     | 20 +++++++++++---------
>  drivers/gpu/drm/sun4i/sun6i_mipi_dsi.h |  2 --
>  2 files changed, 11 insertions(+), 11 deletions(-)
>
> diff --git a/drivers/gpu/drm/sun4i/sun4i_tcon.c
> b/drivers/gpu/drm/sun4i/sun4i_tcon.c
> index 64c43ee6bd92..42560d5c327c 100644
> --- a/drivers/gpu/drm/sun4i/sun4i_tcon.c
> +++ b/drivers/gpu/drm/sun4i/sun4i_tcon.c
> @@ -263,10 +263,11 @@ static int sun4i_tcon_get_clk_delay(const struct
> drm_display_mode *mode,
>  }
>
>  static void sun4i_tcon0_mode_set_common(struct sun4i_tcon *tcon,
> -                                       const struct drm_display_mode *mode)
> +                                       const struct drm_display_mode *mode,
> +                                       u32 tcon_mul)
>  {
>         /* Configure the dot clock */
> -       clk_set_rate(tcon->dclk, mode->crtc_clock * 1000);
> +       clk_set_rate(tcon->dclk, mode->crtc_clock * tcon_mul * 1000);
>
>         /* Set the resolution */
>         regmap_write(tcon->regs, SUN4I_TCON0_BASIC0_REG,
> @@ -335,12 +336,13 @@ static void sun4i_tcon0_mode_set_cpu(struct
> sun4i_tcon *tcon,
>         u8 bpp = mipi_dsi_pixel_format_to_bpp(device->format);
>         u8 lanes = device->lanes;
>         u32 block_space, start_delay;
> -       u32 tcon_div;
> +       u32 tcon_div, tcon_mul;
>
> -       tcon->dclk_min_div = SUN6I_DSI_TCON_DIV;
> -       tcon->dclk_max_div = SUN6I_DSI_TCON_DIV;
> +       tcon->dclk_min_div = 4;
> +       tcon->dclk_max_div = 127;
>
> -       sun4i_tcon0_mode_set_common(tcon, mode);
> +       tcon_mul = bpp / lanes;
> +       sun4i_tcon0_mode_set_common(tcon, mode, tcon_mul);
>
>         /* Set dithering if needed */
>         sun4i_tcon0_mode_set_dithering(tcon, sun4i_tcon_get_connector(encoder));
> @@ -366,7 +368,7 @@ static void sun4i_tcon0_mode_set_cpu(struct
> sun4i_tcon *tcon,
>          */
>         regmap_read(tcon->regs, SUN4I_TCON0_DCLK_REG, &tcon_div);
>         tcon_div &= GENMASK(6, 0);
> -       block_space = mode->htotal * bpp / (tcon_div * lanes);
> +       block_space = mode->htotal * tcon_div * tcon_mul;
>         block_space -= mode->hdisplay + 40;
>
>         regmap_write(tcon->regs, SUN4I_TCON0_CPU_TRI0_REG,
> @@ -408,7 +410,7 @@ static void sun4i_tcon0_mode_set_lvds(struct
> sun4i_tcon *tcon,
>
>         tcon->dclk_min_div = 7;
>         tcon->dclk_max_div = 7;
> -       sun4i_tcon0_mode_set_common(tcon, mode);
> +       sun4i_tcon0_mode_set_common(tcon, mode, 1);
>
>         /* Set dithering if needed */
>         sun4i_tcon0_mode_set_dithering(tcon, sun4i_tcon_get_connector(encoder));
> @@ -487,7 +489,7 @@ static void sun4i_tcon0_mode_set_rgb(struct
> sun4i_tcon *tcon,
>
>         tcon->dclk_min_div = 6;
>         tcon->dclk_max_div = 127;
> -       sun4i_tcon0_mode_set_common(tcon, mode);
> +       sun4i_tcon0_mode_set_common(tcon, mode, 1);
>
>         /* Set dithering if needed */
>         sun4i_tcon0_mode_set_dithering(tcon, connector);
> diff --git a/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.h
> b/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.h
> index 5c3ad5be0690..a07090579f84 100644
> --- a/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.h
> +++ b/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.h
> @@ -13,8 +13,6 @@
>  #include <drm/drm_encoder.h>
>  #include <drm/drm_mipi_dsi.h>
>
> -#define SUN6I_DSI_TCON_DIV     4
> -
>  struct sun6i_dsi {
>         struct drm_connector    connector;
>         struct drm_encoder      encoder;

I had more something like this in mind:
http://code.bulix.org/nlp5a4-803511

You really don't need to change the divider range (or this is another
issue that the one you mentionned).

Maxime

--
Maxime Ripard, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com

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