linux-kernel - Re: [PATCH 1/4] clk: meson: mpll: add init callback and regs

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Date:   Fri, 05 Apr 2019 15:21:35 +0200
From:   Jerome Brunet <jbrunet@...libre.com>
To:     Stephen Boyd <sboyd@...nel.org>,
        Neil Armstrong <narmstrong@...libre.com>
Cc:     linux-amlogic@...ts.infradead.org, linux-clk@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/4] clk: meson: mpll: add init callback and regs

On Fri, 2019-03-29 at 23:58 +0100, Jerome Brunet wrote:
> On Fri, 2019-03-29 at 15:14 -0700, Stephen Boyd wrote:
> > > > We actively discourage using init callbacks. Can you do this some other
> > > > way?
> > > 
> > > Yes I'm aware of that but init it the right place to do this.
> > > To be clear, this is not initializing the clock to some particular rate, the
> > > rate is preserved.
> > > 
> > > It just applies the necessary settings that needs to be done only once to make
> > > sure the clock is in working order and that the rate calculated is actually
> > > accurate. 
> > 
> > Ok, but can you do that in your driver's probe routine instead of
> > attaching to the init callback? We want to get rid of "init" at some
> > point so throwing the init sequence stuff into the driver probe around
> > registration is a solution. Or we should think about not discouraging
> > the init callback
> 
> Is is callback really a problem after all ?
> I think we should actively prevent using it to set a particular rate.
> 
> Here, the goal is put the clock in working order. The bootloader does not
> always do that for us. I could put this in controller driver, but I would have
> to repeat the init pattern for each instance of the clock...not nice 
> Using the callback clearly shows the relationship between the init and the
> clock. I think it is a lot better.
> 
> In the same series, I have added some init for the controller. In this case
> the init target a group of clocks, so having the init in the controller makes
> sense for that
> 
> 

Hi Stephen, Is it ok if we go ahead with this ?

BTW, it is not the only Amlogic clock using the .init callback (the pll and
sclk use it as well). It is not an excuse and I agree, there is always another
way to do things.

Still having an init() callback is really convenient for several cases.
Reworking those 3 drivers to do without it would not help maintainability.