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

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Date:   Thu, 19 Jul 2018 17:37:06 +0200
From:   Maxime Ripard <maxime.ripard@...tlin.com>
To:     Giulio Benetti <giulio.benetti@...ronovasrl.com>
Cc:     Paul Kocialkowski <paul.kocialkowski@...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.

On Wed, Jul 18, 2018 at 04:23:57PM +0200, Giulio Benetti wrote:
> 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>

Applied, thanks

Maxime

-- 
Maxime Ripard, Bootlin (formerly Free Electrons)
Embedded Linux and Kernel engineering
https://bootlin.com

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