linux-kernel - RE: [PATCH] clk: Add functions to get optional clocks

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Date:   Wed, 18 Jul 2018 13:56:26 +0000
From:   Phil Edworthy <phil.edworthy@...esas.com>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>,
        Russell King <linux@...linux.org.uk>
CC:     Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>,
        Simon Horman <horms@...ge.net.au>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        linux-clk <linux-clk@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>
Subject: RE: [PATCH] clk: Add functions to get optional clocks

Hi Russell,

On 18 July 2018 14:19, Geert Uytterhoeven wrote:
> On Wed, Jul 18, 2018 at 3:02 PM Russell King - ARM Linux  wrote:
> > On Wed, Jul 18, 2018 at 01:57:38PM +0100, Phil Edworthy wrote:
> > > Behaves the same as (devm_)clk_get except where there is no clock
> > > producer. In this case, instead of returning -ENOENT, the function
> > > returns NULL. This makes error checking simpler and allows
> > > clk_prepare_enable, etc to be called on the returned reference
> > > without additional checks.
> >
> > How does this work with non-DT systems, where looking a clock up which
> > isn't yet registered with clkdev returns -ENOENT ?
> >
> > (clkdev doesn't know when all clocks are registered with it.)
> 
> Good question.
> 
> I guess all drivers trying to handle optional clocks this way are already broken
> on non-DT systems where clocks may be registered late...

So how do non-DT systems that look a clock up which isn't yet
registered with clkdev, determine that an optional clock is there
or not?

Thanks
Phil