linux-kernel - Re: [PATCH] drm: dw_hdmi: Gate audio sampler clock from the enablement functions

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Message-ID: <20170310094613.GQ21222@n2100.armlinux.org.uk>
Date:   Fri, 10 Mar 2017 09:46:13 +0000
From:   Russell King - ARM Linux <linux@...linux.org.uk>
To:     Romain Perier <romain.perier@...labora.com>
Cc:     Archit Taneja <architt@...eaurora.org>,
        David Airlie <airlied@...ux.ie>,
        Heiko Stuebner <heiko@...ech.de>, linux-kernel@...r.kernel.org,
        dri-devel@...ts.freedesktop.org,
        linux-rockchip@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] drm: dw_hdmi: Gate audio sampler clock from the
 enablement functions

On Fri, Mar 10, 2017 at 10:35:09AM +0100, Romain Perier wrote:
> Currently, the audio sampler clock is enabled from dw_hdmi_setup() at
> step E. and is kept enabled for later use. This clock should be enabled
> and disabled along with the actual audio stream and not always on (that
> is bad for PM). Futhermore, this might cause sound glitches with some
> HDMI devices, as the CTS+N is forced to zero when the stream is disabled
> while the audio clock is still running.
> 
> This commit adds a parameter to hdmi_audio_enable_clk() that controls
> when the audio sample clock must be enabled or disabled. Then, it moves
> the call to this function into dw_hdmi_audio_enable() and
> dw_hdmi_audio_disable().

How does this interact with the workaround given in my commit introducing
these functions?  (Commit b90120a96608).

Setting N=0 is a work-around for iMX6, and we need the audio FIFO to be
loaded with data prior to setting N non-zero.  If disabling the audio
clock prevents the audio FIFO being loaded, your patch will break iMX6.

-- 
RMK's Patch system: http://www.armlinux.org.uk/developer/patches/
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