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References: <20190612085147.26971-1-narmstrong@baylibre.com>
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From:   Doug Anderson <dianders@chromium.org>
Date:   Wed, 19 Jun 2019 14:22:52 -0700
Message-ID: <CAD=FV=UgmMGZHf_Y+GBgQ+fLYGF3yinj3LtLFRhNwABQB6r-qQ@mail.gmail.com>
Subject: Re: [PATCH] drm/bridge: dw-hdmi: Use automatic CTS generation mode
 when using non-AHB audio
To:     Neil Armstrong <narmstrong@baylibre.com>
Cc:     Andrzej Hajda <a.hajda@samsung.com>,
        Laurent Pinchart <Laurent.pinchart@ideasonboard.com>,
        dri-devel <dri-devel@lists.freedesktop.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Jernej Skrabec <jernej.skrabec@siol.net>,
        Maxime Ripard <maxime.ripard@bootlin.com>,
        Jonas Karlman <jonas@kwiboo.se>,
        Heiko Stuebner <heiko@sntech.de>,
        Jerome Brunet <jbrunet@baylibre.com>
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Sender: linux-kernel-owner@vger.kernel.org
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Hi,

On Wed, Jun 12, 2019 at 1:51 AM Neil Armstrong <narmstrong@baylibre.com> wrote:
>
> When using an I2S source using a different clock source (usually the I2S
> audio HW uses dedicated PLLs, different from the HDMI PHY PLL), fixed
> CTS values will cause some frequent audio drop-out and glitches as
> reported on Amlogic, Allwinner and Rockchip SoCs setups.
>
> Setting the CTS in automatic mode will let the HDMI controller generate
> automatically the CTS value to match the input audio clock.
>
> The DesignWare DW-HDMI User Guide explains:
>   For Automatic CTS generation
>   Write "0" on the bit field "CTS_manual", Register 0x3205: AUD_CTS3
>
> The DesignWare DW-HDMI Databook explains :
>   If "CTS_manual" bit equals 0b this registers contains "audCTS[19:0]"
>   generated by the Cycle time counter according to specified timing.
>
> Cc: Jernej Skrabec <jernej.skrabec@siol.net>
> Cc: Maxime Ripard <maxime.ripard@bootlin.com>
> Cc: Jonas Karlman <jonas@kwiboo.se>
> Cc: Heiko Stuebner <heiko@sntech.de>
> Cc: Jerome Brunet <jbrunet@baylibre.com>
> Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
> ---
>  drivers/gpu/drm/bridge/synopsys/dw-hdmi.c | 44 +++++++++++++++--------
>  1 file changed, 29 insertions(+), 15 deletions(-)

Tested-by: Douglas Anderson <dianders@chromium.org>