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Date:   Wed, 12 Apr 2023 03:22:59 +0200
Message-Id: <CRUDUEL17ER4.1R8WRNNB5CJ35@void.crly.cz>
Cc:     "Frank Oltmanns" <frank@oltmanns.dev>,
        "Chen-Yu Tsai" <wens@csie.org>, "David Airlie" <airlied@gmail.com>,
        "Daniel Vetter" <daniel@ffwll.ch>,
        "Samuel Holland" <samuel@sholland.org>,
        <dri-devel@lists.freedesktop.org>,
        <linux-arm-kernel@lists.infradead.org>,
        <linux-sunxi@lists.linux.dev>, <linux-kernel@vger.kernel.org>,
        <icenowy@aosc.io>
Subject: Re: [PATCH] drm/sun4i: uncouple DSI dotclock divider from
 TCON0_DCLK_REG
From:   "Roman Beranek" <romanberanek@icloud.com>
To:     =?utf-8?q?Jernej_=C5=A0krabec?= <jernej.skrabec@gmail.com>,
        "Maxime Ripard" <maxime@cerno.tech>
References: <20230320161636.24411-1-romanberanek@icloud.com>
 <20230329195802.veybo3367zifw77n@penduick>
 <CROTQHUM88W0.2URPO95U5ZMS5@void.crly.cz>
 <2219295.iZASKD2KPV@jernej-laptop>
In-Reply-To: <2219295.iZASKD2KPV@jernej-laptop>
Precedence: bulk

On Sat Apr 8, 2023 at 9:07 AM CEST, Jernej =C5=A0krabec wrote:
> Dne sreda, 05. april 2023 ob 14:34:11 CEST je Roman Beranek napisal(a):
> > While simply forbidding the video0-2x mux option seems
> > to me as the right way to go because there's not much use for it with
> > non-DSI interfaces either besides the opportunity to power pll-mipi
> > down, I'd like to run by you first.
>
> It's been a long time since I looked at A64 HDMI clocks, but IIRC, pll-vi=
deo0=20
> is the only useful source for HDMI PHY (as opposed to HDMI controller.)
> So question remains how to properly support both displays at the same tim=
e.
>

Correct.

> Have you ever tried to make HDMI and DSI work at the same time? This is o=
ne of=20
> issues of the PinePhone IIUC.
>

Yes, I have. Prusa3D's SL1 printer, on which I previously worked on,
uses both outputs simultaneously. I had encountered the same reparenting
problem back then but since I hadn't been able to identify it,
I resorted to fiddling with the DSI pixelclock until it worked.=20

DSI & HDMI co-existence is yet another reasoni though for forbidding
the pll-video-2x parent. megi's kernel includes Mr. Zheng's commit which
does the same.

<https://github.com/megous/linux/commit/7374d57>

Best wishes
Roman Beranek