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Subject: Re: [PATCH] Revert "drm/sun4i: Handle DRM_BUS_FLAG_PIXDATA_*EDGE"
To:     Paul Kocialkowski <paul.kocialkowski@bootlin.com>,
        dri-devel@lists.freedesktop.org,
        linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org
Cc:     Maxime Ripard <maxime.ripard@bootlin.com>,
        David Airlie <airlied@linux.ie>, Chen-Yu Tsai <wens@csie.org>,
        linux-sunxi@googlegroups.com, stable@vger.kernel.org
References: <20180613081647.31183-1-paul.kocialkowski@bootlin.com>
From:   Giulio Benetti <giulio.benetti@micronovasrl.com>
Message-ID: <d5357ae3-9dc1-b0ac-47bf-8742d55c4f3b@micronovasrl.com>
Date:   Wed, 13 Jun 2018 23:52:55 +0200
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Hello,

sorry for my ignorance.
I don't know the right patch workflow in the case of "revert commit".
When I fix this bug, should I have to re-submit the previous patch 
entire plus bug-fix?
Or do I have to submit patch with bug-fix only?

Thanks in advance to everybody

-- 
Giulio Benetti
CTO

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Il 13/06/2018 10:16, Paul Kocialkowski ha scritto:
> This reverts commit 2c17a4368aad2b88b68e4390c819e226cf320f70.
> 
> The offending commit triggers a run-time fault when accessing the panel
> element of the sun4i_tcon structure when no such panel is attached.
> 
> It was apparently assumed in said commit that a panel is always used with
> the TCON. Although it is often the case, this is not always true.
> For instance a bridge might be used instead of a panel.
> 
> This issue was discovered using an A13-OLinuXino, that uses the TCON
> in RGB mode for a simple DAC-based VGA bridge.
> 
> Cc: stable@vger.kernel.org
> Signed-off-by: Paul Kocialkowski <paul.kocialkowski@bootlin.com>
> ---
>   drivers/gpu/drm/sun4i/sun4i_tcon.c | 25 -------------------------
>   1 file changed, 25 deletions(-)
> 
> diff --git a/drivers/gpu/drm/sun4i/sun4i_tcon.c b/drivers/gpu/drm/sun4i/sun4i_tcon.c
> index c3d92d537240..8045871335b5 100644
> --- a/drivers/gpu/drm/sun4i/sun4i_tcon.c
> +++ b/drivers/gpu/drm/sun4i/sun4i_tcon.c
> @@ -17,7 +17,6 @@
>   #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>
>   
> @@ -350,9 +349,6 @@ static void sun4i_tcon0_mode_set_lvds(struct sun4i_tcon *tcon,
>   static void sun4i_tcon0_mode_set_rgb(struct sun4i_tcon *tcon,
>   				     const struct drm_display_mode *mode)
>   {
> -	struct drm_panel *panel = tcon->panel;
> -	struct drm_connector *connector = panel->connector;
> -	struct drm_display_info display_info = connector->display_info;
>   	unsigned int bp, hsync, vsync;
>   	u8 clk_delay;
>   	u32 val = 0;
> @@ -410,27 +406,6 @@ 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 (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);
>