linux-kernel - Re: [PATCH 9/9] clk: imx: add imx7ulp clk driver

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Message-ID: <20170701003511.GR22780@codeaurora.org>
Date:   Fri, 30 Jun 2017 17:35:11 -0700
From:   Stephen Boyd <sboyd@...eaurora.org>
To:     "A.s. Dong" <aisheng.dong@....com>
Cc:     Dong Aisheng <dongas86@...il.com>,
        "linux-clk@...r.kernel.org" <linux-clk@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "mturquette@...libre.com" <mturquette@...libre.com>,
        "shawnguo@...nel.org" <shawnguo@...nel.org>,
        Anson Huang <anson.huang@....com>, Jacky Bai <ping.bai@....com>
Subject: Re: [PATCH 9/9] clk: imx: add imx7ulp clk driver

On 06/21, A.s. Dong wrote:
> > -----Original Message-----
> > From: Stephen Boyd [mailto:sboyd@...eaurora.org]
> > Sent: Wednesday, June 21, 2017 4:42 AM
> > To: Dong Aisheng
> > Cc: A.s. Dong; linux-clk@...r.kernel.org; linux-kernel@...r.kernel.org;
> > linux-arm-kernel@...ts.infradead.org; mturquette@...libre.com;
> > shawnguo@...nel.org; Anson Huang; Jacky Bai
> > Subject: Re: [PATCH 9/9] clk: imx: add imx7ulp clk driver
> > 
> > On 06/20, Dong Aisheng wrote:
> > > On Mon, Jun 19, 2017 at 07:01:19PM -0700, Stephen Boyd wrote:
> > > >
> > > > Any reason why it can't be a platform driver? If not, please add
> > > > some comment explaining why.
> > > >
> > >
> > > Timer is using it at early stage. GIC seems not although standard
> > > binding claim possible clock requirement.
> > > Others still not sure.
> > >
> > > What your suggestion?
> > > Convert timer to platform driver and make clock as platform driver as
> > well?
> > >
> > 
> > The timer can't be a platform driver because it would be too late. The
> > clock driver could register whatever clks are required for the timer/GIC
> > in a CLK_OF_DECLARE_DRIVER hook, and then leave the rest to a platform
> > driver. This way we get some of the device driver framework in this code.
> > 
> 
> Okay, I could try it. Thanks.
> 
> One thing is that TPM clock has a lot parents and parents having parents,
> as well as PIT timer. So I may need enable more than half clocks in
> CLK_OF_DECLARE_DRIVER hook.

That's fine.

> 
> BTW, What's benefit to convert into two parts of probe?
> I'm not quite if I already get it all, can you help clarify it?
> 

The benefit is that we still get a platform driver and we can
associate a device pointer with the clock controller eventually.
Here's a reply I sent yesterday on the same topic:

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 (this one doesn't
     apply here)

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