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

From: Ulf Hansson <ulf.hansson@linaro.org>
To: Jerome Brunet <jbrunet@baylibre.com>,
	Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Cc: Stephen Boyd <sboyd@kernel.org>,
	"open list:ARM/Amlogic Meson..."
	<linux-amlogic@lists.infradead.org>,
	"linux-mmc@vger.kernel.org" <linux-mmc@vger.kernel.org>,
	DTML <devicetree@vger.kernel.org>,
	Rob Herring <robh+dt@kernel.org>,
	Jianxin Pan <jianxin.pan@amlogic.com>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	yinxin_1989@aliyun.com,
	Linux ARM <linux-arm-kernel@lists.infradead.org>,
	lnykww@gmail.com, Anand Moon <linux.amoon@gmail.com>
Subject: Re: [PATCH v6 2/2] mmc: host: meson-mx-sdhc: new driver for the Amlogic Meson SDHC host
Date: Tue, 5 May 2020 10:17:15 +0200	[thread overview]
Message-ID: <CAPDyKFq_USCNNps3s4+C_1hriycrxtRMKJvnPFcP59CZmLXbGw@mail.gmail.com> (raw)
In-Reply-To: <1jh7x1i3hj.fsf@starbuckisacylon.baylibre.com>

[...]

> >> > +
> >> > +     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.

[...]

Kind regards
Uffe

[1]
https://www.spinics.net/lists/linux-clk/msg48373.html