linux-kernel - Re: [PATCH v6 2/2] mmc: host: meson-mx-sdhc: new driver for the Amlogic Meson SDHC host

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Date:   Tue, 5 May 2020 19:30:59 +0200
From:   Ulf Hansson <ulf.hansson@...aro.org>
To:     Jerome Brunet <jbrunet@...libre.com>
Cc:     Martin Blumenstingl <martin.blumenstingl@...glemail.com>,
        Stephen Boyd <sboyd@...nel.org>,
        "open list:ARM/Amlogic Meson..." <linux-amlogic@...ts.infradead.org>,
        "linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>,
        DTML <devicetree@...r.kernel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Jianxin Pan <jianxin.pan@...ogic.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        yinxin_1989@...yun.com,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        lnykww@...il.com, Anand Moon <linux.amoon@...il.com>
Subject: Re: [PATCH v6 2/2] mmc: host: meson-mx-sdhc: new driver for the
 Amlogic Meson SDHC host

On Tue, 5 May 2020 at 18:05, Jerome Brunet <jbrunet@...libre.com> wrote:
>
>
> On Tue 05 May 2020 at 10:17, Ulf Hansson <ulf.hansson@...aro.org> wrote:
>
> > [...]
> >
> >> >> > +
> >> >> > +     return devm_of_clk_add_hw_provider(dev, of_clk_hw_onecell_get,
> >> >> > +                                        onecell_data);
> >> >>
> >> >> I think registering a provider for a module that does not provide clocks
> >> >> to any other device is a bit overkill.
> >> >>
> >> >> I understand the matter is getting the per-user clk* pointer.
> >> >> Since this is the module registering the clock, you can use clk_hw->clk
> >> >> to get it.
> >> >>
> >> >> Once you have the clk* of the leaf clocks, you don't even need to keep
> >> >> track of the clk_hw* since you are using devm_
> >> >>
> >> >> Afterward, we should propably discuss with Stephen if something should
> >> >> be added in CCF to get a struct clk* from struct clk_hw*.
> >> >>
> >> >
> >> > [...]
> >> >
> >> > Hmm.
> >> >
> >> > I am not sure the above is a good idea, at all. Unless, I am
> >> > misunderstanding your point, which may be the case.
> >> >
> >> > I think above "shortcuts" could lead to abuse of the clock framework
> >> > and its internal data structures. When going forward, this could make
> >> > it unnecessary harder to maintain the clock framework.
> >> >
> >> > I know, it's not my responsibility, but from my experience with MMC
> >> > and SDIO interfaces, is that those have been too easy abuse - since
> >> > most of the data structures and interfaces have been exported. Now,
> >> > it's hard to roll back that, if you see what I mean.
> >>
> >> Indeed, it worth clarifying this first.
> >>
> >> With clk_register deprecated in favor of clk_hw_register, we are likely
> >> to see that case rise elsewhere.
> >>
> >
> > So, according to the separate discussion [1], I think we can let
> > Martin decide what option to implement at this point.
> >
> > 1. Implement the "clk_hw_get_clk()" approach. The preferred option,
> > but requires wider changes of the clock subsystem as well.
> >
> > 2. Keep the existing approach, with devm_clk_get(). I am fine with
> > this as well, we can always switch to 1) later on.
>
> I have a problem with this approach.
> The dt-bindings would include "#clock-cells = <1>" for a device that
> does not actually provide and only needs it has a temporary work around.
> Those bindings are supposed to be stable ...

I agree, the bindings need to be stable.

What is the problem of keeping "#clock-cells = <1>" around, when we
move to a clk_hw_get_clk() approach in the next step?

>
> I have proposed 2 other short term solutions, let's see how it goes

Yes, seems like we need to wait for Stephen's input then.

Kind regards
Uffe