linux-kernel - Re: [PATCH 0/3] Apple M1 clock gate driver

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Date:   Wed, 2 Jun 2021 12:26:08 +0300
From:   Tony Lindgren <tony@...mide.com>
To:     Sven Peter <sven@...npeter.dev>
Cc:     Rob Herring <robh+dt@...nel.org>, devicetree@...r.kernel.org,
        linux-clk <linux-clk@...r.kernel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Hector Martin <marcan@...can.st>,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>,
        Mark Kettenis <mark.kettenis@...all.nl>,
        Arnd Bergmann <arnd@...nel.org>
Subject: Re: [PATCH 0/3] Apple M1 clock gate driver

* Sven Peter <sven@...npeter.dev> [210530 11:09]:
> Hi,
> 
> On Wed, May 26, 2021, at 09:18, Tony Lindgren wrote:
> > Hi,
> > 
> > * Rob Herring <robh+dt@...nel.org> [210525 18:09]:
> > > I would do a single node per mmio region with the register offset (or
> > > offset / 4) being the clock id. This can still support new SoCs easily
> > > if you have a fallback compatible. If you want/need to get all the
> > > clocks, just walk the DT 'clocks' properties and extract all the IDs.
> > 
> > I mostly agree.. Except I'd also leave out the artificial clock ID and
> > just use real register offsets from the clock controller base instead.
> 
> Sure, I'll do that.
> 
> > 
> > So a single clock controller node for each MMIO range, then set
> > #clock=cells = <1>. Then the binding follows what we have for the
> > interrupts-extended binding for example.
> > 
> > If the clock controller optionally needs some data in the dts,
> > that can be added to the clock controller node. Or it can be driver
> > internal built-in data. If the data for dts can be described in a
> > generic way, even better :)
> 
> Now the big question is *how* to describe this additional data in the
> dts. Essentially I need to specify that e.g. to enable clock 0x270
> I first need to enable the (internal) clocks 0x1c0 and then 0x220.
> Are you aware of any generic way to describe this? I'm not even sure
> how a sane non-generic way would look like when I just have a single
> clock controller node.

To me it seems you might be able to recycle the assigned-clocks and
assigned-clock-parents etc properties in the clock controller node.

Sure the assigned-clocks property will point to clocks in the
clock controller itself, and will have tens of entries, but should
work :)

And sounds like you can generate that list with some script from the
Apple dtb.

Regards,

Tony