Re: [PATCH v2 1/2] drm/bridge/synopsys: dw-hdmi: Handle audio for more clock rates

From: Doug Anderson <dianders@chromium.org>
To: Andrzej Hajda <a.hajda@samsung.com>
Cc: "Laurent Pinchart" <Laurent.pinchart@ideasonboard.com>,
	"Sean Paul" <seanpaul@chromium.org>,
	"Jernej Skrabec" <jernej.skrabec@siol.net>,
	"Heiko Stübner" <heiko@sntech.de>,
	"Jonas Karlman" <jonas@kwiboo.se>,
	"Maxime Ripard" <maxime.ripard@bootlin.com>,
	"Neil Armstrong" <narmstrong@baylibre.com>,
	"open list:ARM/Rockchip SoC..."
	<linux-rockchip@lists.infradead.org>,
	"Dylan Reid" <dgreid@chromium.org>,
	"Cheng-Yi Chiang" <cychiang@chromium.org>,
	"Jerome Brunet" <jbrunet@baylibre.com>,
	"Sam Ravnborg" <sam@ravnborg.org>,
	dri-devel <dri-devel@lists.freedesktop.org>,
	LKML <linux-kernel@vger.kernel.org>,
	"David Airlie" <airlied@linux.ie>,
	"Daniel Vetter" <daniel@ffwll.ch>
Subject: Re: [PATCH v2 1/2] drm/bridge/synopsys: dw-hdmi: Handle audio for more clock rates
Date: Wed, 26 Jun 2019 12:24:32 -0700	[thread overview]
Message-ID: <CAD=FV=VNR1z_WL7rrfv-O5cXFjDowq3qZe-3tg9o9YHjQgyCAA@mail.gmail.com> (raw)
In-Reply-To: <a94d9554-fc93-a2d0-9a30-9604db8c123e@samsung.com>

Hi,

On Wed, Jun 26, 2019 at 2:56 AM Andrzej Hajda <a.hajda@samsung.com> wrote:
>
> >   AKA: anyone using auto-CTS won't notice any change
> > at all.  I guess the question is: with Auto-CTS should you pick the
> > "ideal" 6272 or a value that allows CTS to be the closest to integral
> > as possible.  By reading between the lines of the spec, I decided that
> > it was slightly more important to allow for an integral CTS.  If
> > achieving an integral CTS wasn't a goal then the spec wouldn't even
> > have listed special cases for any of the clock rates.  We would just
> > be using the ideal N and Auto-CTS and be done with it.  The whole
> > point of the tables they list is to make CTS integral.
>
>
> Specification recommends many contradictory things without explicit
> prioritization, at least I have not found it.
>
> So we should relay on our intuition.
>
> I guess that with auto-cts N we should follow recommendation - I guess
> most sinks have been better tested with recommended values.
>
> So what with non-auto-cts case:
>
> 1. How many devices do not have auto-cts? how many alternative TMDS
> clocks we have? Maybe it is theoretical problem.
>
> 2. Alternating CTS in software is possible, but quite
> complicated/annoying, but at least it will follow recommendation :)

It is OK w/ me if we want to drop my patch.  With the auto-CTS patch
it shouldn't matter anymore.  ...but I still wanted to post it to the
list for posterity in case it is ever useful for someone else.

-Doug