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

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Message-ID: <20180905143932.lbytjftmobjtzdsu@flea>
Date:   Wed, 5 Sep 2018 16:39:32 +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-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        linux-sunxi@...glegroups.com, 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 04:05:18PM +0800, Icenowy Zheng wrote:
> 
> 
> 于 2018年9月5日 GMT+08:00 下午3:56:01, Maxime Ripard <maxime.ripard@...tlin.com> 写到:
> >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.
> 
> Then how to deal with double PLL support? Make them temporarily
> dead during 4.19?

Well, if the PHY doesn't use two PLL, don't use it, ever. Why does it
have to be temporary?

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

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