Re: [PATCH 5/5] drm/sun4i: Run the mixer clock at 297 MHz on V3s

Icenowy Zheng
2025-07-02T02:55:38Z

在 2025-07-01星期二的 22:11 +0200，Paul Kocialkowski写道：
> The DE mixer clock is currently set to run at 150 MHz, while the
> Allwinner BSP configures it at 300 MHz and other platforms typically
> run at 297 MHz.
>
> 150 MHz appears to be enough given the restricted graphics
> capabilities
> of the SoC (with a work area of only 1024x1024). However it typically
> causes the DE clock to be parented to the periph0 pll instead of the
> video PLL.
>
> While this should generally not be a concern, it appears (based on
> experimentation) that both the DE and TCON clocks need to be parented
> to the same PLL for these units to work. While we cannot represent
> this
> constraint in the clock driver, it appears that the TCON clock will
> often get parented to the video pll (typically running at 297 MHz for

Ah I think pixel clocks are arbitary and nothing could be predicted
about it...

> the CSI units needs), for instance when driving displays with a 33
> MHz
> pixel clock (33 being a natural divider of 297).
>
> Running the DE clock at 297 MHz will typically result in parenting to
> the video pll instead of the periph0 pll, thus making the display
> output functional.
>
> This is all a bit fragile but it solves the issue with displays
> running
> at 33 Mhz and brings V3s to use the same frequency as other
> platforms,
> making support more unified.
>
> Also align and sort the fields of the v3s mixer config while at it.
>
> Signed-off-by: Paul Kocialkowski <paulk@sys-base.io>
> ---
>  drivers/gpu/drm/sun4i/sun8i_mixer.c | 12 ++++++------
>  1 file changed, 6 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/gpu/drm/sun4i/sun8i_mixer.c
> b/drivers/gpu/drm/sun4i/sun8i_mixer.c
> index 8b41d33baa30..35fdc2451060 100644
> --- a/drivers/gpu/drm/sun4i/sun8i_mixer.c
> +++ b/drivers/gpu/drm/sun4i/sun8i_mixer.c
> @@ -670,12 +670,12 @@ static const struct sun8i_mixer_cfg
> sun8i_r40_mixer1_cfg = {
>  };
>
>  static const struct sun8i_mixer_cfg sun8i_v3s_mixer_cfg = {
> -       .vi_num = 2,
> -       .ui_num = 1,
> -       .scaler_mask = 0x3,
> -       .scanline_yuv = 2048,
> -       .ccsc = CCSC_MIXER0_LAYOUT,
> -       .mod_rate = 150000000,
> +       .ccsc           = CCSC_MIXER0_LAYOUT,
> +       .mod_rate       = 297000000,
> +       .scaler_mask    = 0x3,
> +       .scanline_yuv   = 2048,
> +       .ui_num         = 1,
> +       .vi_num         = 2,
>  };
>
>  static const struct sun8i_mixer_cfg sun20i_d1_mixer0_cfg = {