linux-kernel - Re: [PATCH] drm/sun4i: Handle DRM_BUS_FLAG_PIXDATA

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Message-ID: <e1fcedb1-64d5-24fb-ffc1-d418620ec795@micronovasrl.com>
Date:   Wed, 18 Jul 2018 16:42:25 +0200
From:   Giulio Benetti <giulio.benetti@...ronovasrl.com>
To:     Paul Kocialkowski <paul.kocialkowski@...tlin.com>
Cc:     Maxime Ripard <maxime.ripard@...tlin.com>,
        David Airlie <airlied@...ux.ie>, Chen-Yu Tsai <wens@...e.org>,
        "open list:DRM DRIVERS FOR ALLWINNER A10" 
        <dri-devel@...ts.freedesktop.org>,
        "moderated list:ARM/Allwinner sunXi SoC support" 
        <linux-arm-kernel@...ts.infradead.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] drm/sun4i: Handle DRM_BUS_FLAG_PIXDATA_*EDGE checking if
 panel is used.

Hi Paul,

can you give a try to this patch on A13 with VGA DAC?
Unfortunately I don't have an A13 board to test it.

Thanks in advance.

Giulio

Il 18/07/2018 16:23, Giulio Benetti ha scritto:
> Handle both positive and negative dclk polarity,
> according to bus_flags, taking care of this:
> 
> On A20 and similar SoCs, the only way to achieve Positive Edge
> (Rising Edge), is setting dclk clock phase to 2/3(240°).
> By default TCON works in Negative Edge(Falling Edge), this is why phase
> is set to 0 in that case.
> Unfortunately there's no way to logically invert dclk through IO_POL
> register.
> The only acceptable way to work, triple checked with scope,
> is using clock phase set to 0° for Negative Edge and set to 240° for
> Positive Edge.
> On A33 and similar SoCs there would be a 90° phase option, but it divides
> also dclk by 2.
> This patch is a way to avoid quirks all around TCON and DOTCLOCK drivers
> for using A33 90° phase divided by 2 and consequently increase code
> complexity.
> 
> Check if panel is used. TCON can also handle VGA DAC, then panel could
> be empty.
> 
> Signed-off-by: Giulio Benetti <giulio.benetti@...ronovasrl.com>
> ---
>   drivers/gpu/drm/sun4i/sun4i_tcon.c | 28 ++++++++++++++++++++++++++++
>   1 file changed, 28 insertions(+)
> 
> diff --git a/drivers/gpu/drm/sun4i/sun4i_tcon.c b/drivers/gpu/drm/sun4i/sun4i_tcon.c
> index 8232b39e16ca..5c7d6ae53111 100644
> --- a/drivers/gpu/drm/sun4i/sun4i_tcon.c
> +++ b/drivers/gpu/drm/sun4i/sun4i_tcon.c
> @@ -17,6 +17,7 @@
>   #include <drm/drm_encoder.h>
>   #include <drm/drm_modes.h>
>   #include <drm/drm_of.h>
> +#include <drm/drm_panel.h>
>   
>   #include <uapi/drm/drm_mode.h>
>   
> @@ -474,6 +475,33 @@ static void sun4i_tcon0_mode_set_rgb(struct sun4i_tcon *tcon,
>   	if (mode->flags & DRM_MODE_FLAG_PVSYNC)
>   		val |= SUN4I_TCON0_IO_POL_VSYNC_POSITIVE;
>   
> +	/*
> +	 * On A20 and similar SoCs, the only way to achieve Positive Edge
> +	 * (Rising Edge), is setting dclk clock phase to 2/3(240°).
> +	 * By default TCON works in Negative Edge(Falling Edge),
> +	 * this is why phase is set to 0 in that case.
> +	 * Unfortunately there's no way to logically invert dclk through
> +	 * IO_POL register.
> +	 * The only acceptable way to work, triple checked with scope,
> +	 * is using clock phase set to 0° for Negative Edge and set to 240°
> +	 * for Positive Edge.
> +	 * On A33 and similar SoCs there would be a 90° phase option,
> +	 * but it divides also dclk by 2.
> +	 * Following code is a way to avoid quirks all around TCON
> +	 * and DOTCLOCK drivers.
> +	 */
> +	if (!IS_ERR(tcon->panel)) {
> +		struct drm_panel *panel = tcon->panel;
> +		struct drm_connector *connector = panel->connector;
> +		struct drm_display_info display_info = connector->display_info;
> +
> +		if (display_info.bus_flags & DRM_BUS_FLAG_PIXDATA_POSEDGE)
> +			clk_set_phase(tcon->dclk, 240);
> +
> +		if (display_info.bus_flags & DRM_BUS_FLAG_PIXDATA_NEGEDGE)
> +			clk_set_phase(tcon->dclk, 0);
> +	}
> +
>   	regmap_update_bits(tcon->regs, SUN4I_TCON0_IO_POL_REG,
>   			   SUN4I_TCON0_IO_POL_HSYNC_POSITIVE | SUN4I_TCON0_IO_POL_VSYNC_POSITIVE,
>   			   val);
>