linux-kernel - Re: [PATCH 1/3] dt-bindings: change the A64 HDMI PHY binding to R40

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Message-ID: <20180905075601.32kzkd3is2gpa3ft@flea>
Date:   Wed, 5 Sep 2018 09:56:01 +0200
From:   Maxime Ripard <maxime.ripard@...tlin.com>
To:     Icenowy Zheng <icenowy@...c.io>
Cc:     linux-arm-kernel@...ts.infradead.org, devicetree@...r.kernel.org,
        Jernej Skrabec <jernej.skrabec@...l.net>,
        linux-sunxi@...glegroups.com, linux-kernel@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, Chen-Yu Tsai <wens@...e.org>
Subject: Re: [PATCH 1/3] dt-bindings: change the A64 HDMI PHY binding to R40

On Wed, Sep 05, 2018 at 03:46:41PM +0800, Icenowy Zheng wrote:
> 
> 
> 于 2018年9月5日 GMT+08:00 下午3:14:35, Maxime Ripard <maxime.ripard@...tlin.com> 写到:
> >On Mon, Sep 03, 2018 at 09:34:32PM +0800, Icenowy Zheng wrote:
> >> By experiment, the A64 HDMi PHY doesn't support the PLL-VIDEO mux
> >> introduced in R40, although it has two PLL-VIDEOs.
> >> 
> >> Change the A64 HDMI PHY binding to R40 one.
> >> 
> >> This binding is introduced in v4.19, which is still in RC stage, so
> >we
> >> have change to fix it.
> >> 
> >> Signed-off-by: Icenowy Zheng <icenowy@...c.io>
> >
> >That doesn't make much sense. The A64 doesn't have any particular
> >reason to behave like the R40, and the R40 can definitely use a
> >different compatible if it has a different behaviour. But I don't see
> >*why* the A64 not behaving like the R40 is a justification to remove
> >the A64 compatible. Especially when the R40 was released later.
> >
> >Add a new compatible, and leave the A64 compatible alone.
> 
> But the behavior of A64 compatible will change from double
> PLL to single PLL, because the A64 HDMI PHY is proven
> to have no double PLL.
> 
> Should I then change the A64 compatible behavior and import R40
> compatible at the same time?

I don't see why you should do both at the same time. Fix the A64, and
add the support for the R40, those are two orthogonal changes.

> In addition maybe I can just drop A64 compatible, and let A64
> use H3 one.

No, that break the backward compatibility.

Maxime

-- 
Maxime Ripard, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com

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