linux-kernel - Re: [PATCH 07/14] clock: milbeaut: Add Milbeaut M10V clock control

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Message-ID: <154595756614.179992.794211301759568891@swboyd.mtv.corp.google.com>
Date:   Thu, 27 Dec 2018 16:39:26 -0800
From:   Stephen Boyd <sboyd@...nel.org>
To:     "Sugaya, Taichi" <sugaya.taichi@...ionext.com>,
        devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-clk@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-serial@...r.kernel.org
Cc:     Michael Turquette <mturquette@...libre.com>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Russell King <linux@...linux.org.uk>,
        Jiri Slaby <jslaby@...e.com>,
        Masami Hiramatsu <masami.hiramatsu@...aro.org>,
        Jassi Brar <jaswinder.singh@...aro.org>
Subject: Re: [PATCH 07/14] clock: milbeaut: Add Milbeaut M10V clock control

Quoting Sugaya, Taichi (2018-12-25 17:35:27)
> Hi
> 
> On 2018/11/30 17:31, Stephen Boyd wrote:
> >> +       init.num_parents = parents;
> >> +       init.parent_names = parent_names;
> >> +
> >> +       mcm->cname = clk_name;
> >> +       mcm->parent = 0;
> >> +       mcm->hw.init = &init;
> >> +
> >> +       clk = clk_register(NULL, &mcm->hw);
> >> +       if (IS_ERR(clk))
> >> +               goto err_clk;
> >> +
> >> +       of_clk_add_provider(node, of_clk_src_simple_get, clk);
> >> +       return;
> >> +
> >> +err_clk:
> >> +       kfree(mcm);
> >> +err_mcm:
> >> +       kfree(parent_names);
> >> +}
> >> +CLK_OF_DECLARE(m10v_clk_mux, "socionext,milbeaut-m10v-clk-mux",
> >> +                       m10v_clk_mux_setup);
> > 
> > Any chance you can use a platform driver?
> > 
> 
> Excuse me to re-ask you.
> Why do you recommend to use a platform driver? Is that current fad?

Not exactly a fad. We've been doing it for some time now. From an older
email on the list:

Reasons (in no particular order):

  1. We get a dev pointer to use with clk_hw_register()

  2. We can handle probe defer if some resource is not available

  3. Using device model gets us a hook into power management frameworks
     like runtime PM and system PM for things like suspend and hibernate

  4. It encourages a single DT node clk controller style binding
     instead of a single node per clk style binding

  5. We can use non-DT specific functions like devm_ioremap_resource() to map
     registers and acquire other resources, leading to more portable and
     generic code

  6. We may be able to make the device driver a module, which will
     make distros happy if we don't have to compile in all
     these clk drivers to the resulting vmlinux