Re: [PATCH 2/5] drm/sun4i: tcon: set sync polarity for tcon1 channel

[Chen-Yu Tsai <wens@csie.org>]

On Fri, Feb 5, 2021 at 2:48 AM Jernej Skrabec <jernej.skrabec@siol.net> wrote:
>
> Channel 1 has polarity bits for vsync and hsync signals but driver never
> sets them. It turns out that with pre-HDMI2 controllers seemingly there
> is no issue if polarity is not set. However, with HDMI2 controllers
> (H6) there often comes to de-synchronization due to phase shift. This
> causes flickering screen. It's safe to assume that similar issues might
> happen also with pre-HDMI2 controllers.
>
> Solve issue with setting vsync and hsync polarity. Note that display
> stacks with tcon top have polarity bits actually in tcon0 polarity
> register.
>
> Fixes: 9026e0d122ac ("drm: Add Allwinner A10 Display Engine support")
> Tested-by: Andre Heider <a.heider@gmail.com>
> Signed-off-by: Jernej Skrabec <jernej.skrabec@siol.net>
> ---
>  drivers/gpu/drm/sun4i/sun4i_tcon.c | 24 ++++++++++++++++++++++++
>  drivers/gpu/drm/sun4i/sun4i_tcon.h |  5 +++++
>  2 files changed, 29 insertions(+)
>
> diff --git a/drivers/gpu/drm/sun4i/sun4i_tcon.c b/drivers/gpu/drm/sun4i/sun4i_tcon.c
> index 6b9af4c08cd6..0d132dae58c0 100644
> --- a/drivers/gpu/drm/sun4i/sun4i_tcon.c
> +++ b/drivers/gpu/drm/sun4i/sun4i_tcon.c
> @@ -672,6 +672,29 @@ static void sun4i_tcon1_mode_set(struct sun4i_tcon *tcon,
>                      SUN4I_TCON1_BASIC5_V_SYNC(vsync) |
>                      SUN4I_TCON1_BASIC5_H_SYNC(hsync));
>
> +       /* Setup the polarity of sync signals */
> +       if (tcon->quirks->polarity_in_ch0) {
> +               val = 0;
> +
> +               if (mode->flags & DRM_MODE_FLAG_PHSYNC)
> +                       val |= SUN4I_TCON0_IO_POL_HSYNC_POSITIVE;
> +
> +               if (mode->flags & DRM_MODE_FLAG_PVSYNC)
> +                       val |= SUN4I_TCON0_IO_POL_VSYNC_POSITIVE;
> +
> +               regmap_write(tcon->regs, SUN4I_TCON0_IO_POL_REG, val);
> +       } else {
> +               val = SUN4I_TCON1_IO_POL_UNKNOWN;

I think a comment for the origin of this is warranted.

Otherwise,

Reviewed-by: Chen-Yu Tsai <wens@csie.org>

> +
> +               if (mode->flags & DRM_MODE_FLAG_PHSYNC)
> +                       val |= SUN4I_TCON1_IO_POL_HSYNC_POSITIVE;
> +
> +               if (mode->flags & DRM_MODE_FLAG_PVSYNC)
> +                       val |= SUN4I_TCON1_IO_POL_VSYNC_POSITIVE;
> +
> +               regmap_write(tcon->regs, SUN4I_TCON1_IO_POL_REG, val);
> +       }
> +
>         /* Map output pins to channel 1 */
>         regmap_update_bits(tcon->regs, SUN4I_TCON_GCTL_REG,
>                            SUN4I_TCON_GCTL_IOMAP_MASK,
> @@ -1500,6 +1523,7 @@ static const struct sun4i_tcon_quirks sun8i_a83t_tv_quirks = {
>
>  static const struct sun4i_tcon_quirks sun8i_r40_tv_quirks = {
>         .has_channel_1          = true,
> +       .polarity_in_ch0        = true,
>         .set_mux                = sun8i_r40_tcon_tv_set_mux,
>  };
>
> diff --git a/drivers/gpu/drm/sun4i/sun4i_tcon.h b/drivers/gpu/drm/sun4i/sun4i_tcon.h
> index c5ac1b02482c..b504fb2d3de5 100644
> --- a/drivers/gpu/drm/sun4i/sun4i_tcon.h
> +++ b/drivers/gpu/drm/sun4i/sun4i_tcon.h
> @@ -154,6 +154,10 @@
>  #define SUN4I_TCON1_BASIC5_V_SYNC(height)              (((height) - 1) & 0x3ff)
>
>  #define SUN4I_TCON1_IO_POL_REG                 0xf0
> +#define SUN4I_TCON1_IO_POL_UNKNOWN                     BIT(26)
> +#define SUN4I_TCON1_IO_POL_HSYNC_POSITIVE              BIT(25)
> +#define SUN4I_TCON1_IO_POL_VSYNC_POSITIVE              BIT(24)
> +
>  #define SUN4I_TCON1_IO_TRI_REG                 0xf4
>
>  #define SUN4I_TCON_ECC_FIFO_REG                        0xf8
> @@ -236,6 +240,7 @@ struct sun4i_tcon_quirks {
>         bool    needs_de_be_mux; /* sun6i needs mux to select backend */
>         bool    needs_edp_reset; /* a80 edp reset needed for tcon0 access */
>         bool    supports_lvds;   /* Does the TCON support an LVDS output? */
> +       bool    polarity_in_ch0; /* some tcon1 channels have polarity bits in tcon0 pol register */
>         u8      dclk_min_div;   /* minimum divider for TCON0 DCLK */
>
>         /* callback to handle tcon muxing options */
> --
> 2.30.0
>

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