linux-kernel - Re: [PATCH RFC RFT 3/3] clk: introduce CLK_ENABLE_HAND

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Date:	Tue, 11 Aug 2015 13:03:12 +0100
From:	Lee Jones <lee.jones@...aro.org>
To:	Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:	Maxime Coquelin <maxime.coquelin@...com>,
	Michael Turquette <mturquette@...libre.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	linux-clk@...r.kernel.org, Stephen Boyd <sboyd@...eaurora.org>,
	Maxime Ripard <maxime.ripard@...e-electrons.com>,
	Sascha Hauer <s.hauer@...gutronix.de>
Subject: Re: [PATCH RFC RFT 3/3] clk: introduce CLK_ENABLE_HAND_OFF flag

On Tue, 11 Aug 2015, Geert Uytterhoeven wrote:

> Hi Maxime,
> 
> On Tue, Aug 11, 2015 at 1:41 PM, Maxime Coquelin <maxime.coquelin@...com> wrote:
> > On 08/11/2015 01:36 PM, Maxime Coquelin wrote:
> >> On 08/11/2015 12:11 PM, Geert Uytterhoeven wrote:
> >>> On Tue, Aug 11, 2015 at 12:02 PM, Maxime Coquelin
> >>> <maxime.coquelin@...com> wrote:
> >>>> How can we pass CLK_ENABLE_HAND_OFF flag to a specific clock on STi
> >>>> platform?
> >>>
> >>> Add the flag to the relevant clocks in the C code, e.g. in
> >>> clk_register_flexgen():
> >>>
> >>>          if (!strcmp(name, "clk-icn-cpu"))
> >>>                  init.flags |= CLK_ENABLE_HAND_OFF;
> >
> > The main problem I see with this proposal is that clk_register_flexgen() is
> > called for several SoCs (STiH407/410/418...).
> > Each of these SoCs have this clock, but maybe STiH407 will need the flag,
> > but not STiH410 and STiH418.
> > So I think the best place to set this information is in DT, where the
> > differentiation is made between the SoCs.
> 
> If (of_machine_is_compatible("st,stih410")) ...

This is getting very messy.

Ideally we'd like to keep platform code out of device drivers.
Critical clock description belongs in DT for our use-case.  We can
write code to extract the information from there and set the flag is
Mike's solution is deemed appropriate.

With regards to your "Software Policy Vs Hardware Description"
comment; we already have 10's of "Software Policy" bindings which do
not describe hardware in the purest sense; frequency specifications,
line/voltage levels, GPIO configuration, the list goes on.

-- 
Lee Jones
Linaro STMicroelectronics Landing Team Lead
Linaro.org │ Open source software for ARM SoCs
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