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From: Lee Jones <lee.jones@linaro.org>
To: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Mike Turquette <mturquette@linaro.org>,
	"linux-arm-kernel@lists.infradead.org" 
	<linux-arm-kernel@lists.infradead.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	kernel@stlinux.com, Stephen Boyd <sboyd@codeaurora.org>,
	"devicetree@vger.kernel.org" <devicetree@vger.kernel.org>
Subject: Re: [PATCH v3 0/4] clk: st: New always-on clock domain
Date: Thu, 2 Apr 2015 11:48:38 +0100	[thread overview]
Message-ID: <20150402104838.GZ9447@x1> (raw)
In-Reply-To: <CAMuHMdWYEWoCkARLjU3WXWyh+tbe=j_ftAF+HDFT6dYAfcCo-w@mail.gmail.com>

On Thu, 02 Apr 2015, Geert Uytterhoeven wrote:
> On Thu, Mar 26, 2015 at 8:38 PM, Lee Jones <lee.jones@linaro.org> wrote:
> > On Thu, 26 Mar 2015, Geert Uytterhoeven wrote:
> >> On Thu, Mar 26, 2015 at 2:51 PM, Lee Jones <lee.jones@linaro.org> wrote:
> >> > On Wed, 25 Mar 2015, Geert Uytterhoeven wrote:
> >> >> On Mon, Mar 9, 2015 at 10:28 AM, Lee Jones <lee.jones@linaro.org> wrote:
> >> >> > On Fri, 06 Mar 2015, Mike Turquette wrote:
> >> >> >> This approach looks fine to me. In practice I think it is restricted to
> >> >> >> hardware blocks that don't exist in DT yet (e.g. no driver, in the case
> >> >> >> of your interconnect) and that restriction is probably for the best.
> >> >> >
> >> >> > Agreed.
> >> >>
> >> >> I think this restriction should be documented in the DT binding more clearly,
> >> >> as adding a "clk-always-on" node prohibits you from handling the clock
> >> >> correctly in
> >> >> the future.
> >> >
> >> > Would you mind taking the time to explain what you think those
> >> > limitations are?
> >>
> >> If you add a "clk-always-on" node, the clock will always on using that DT.
> >> That will still be true later, when you get a better understanding of the
> >> hardware, and might discover you're gonna need a driver for the currently
> >> hidden core component that's driven by the clock, and may want to manage
> >> that clock.
> >
> > So I have two points here.
> >
> > First point; I think you're looking at an older version of my set.
> > The newer one can be found at [1] and no longer uses 'always-on'
> > nodes.  Instead the 'clk-always-on' property is applied to the
> > provider.  See the documentation patch [2] for more details.
> 
> Thanks, I was indeed looking at an old version.
> Still, that doesn't change that the clock to not be disabled in specified
> explicitly from DT.
> 
> > Second point; this binding is _not_ to be used as a hack because the
> > hardware isn't understood.  Genuine uses are for clocks that must not
> > be turned off ever, else bad things will happen.  If the hardware is
> > not understood, use 'clk-disable-unused' on the kernel cmdline
> > instead.

[...]

> > If this clock should _genuinely_ be always-on, then use my new
> > binding in the clock controller node and the Clk framework will not
> > turn it off.
> 
> It's supposed to be on when the application ARM core(s) is/are running.
> Many SoCs also have smaller cores (SH, Cortex R or M), intended to
> run a real-time OS. If the RT core is in charge, it may decide to shut down
> the application ARM core(s), incl. supposedly always-on modules like
> the ARM GIC.
> 
> I couldn't find a detailed block diagram of the STiH4xx SoCs, but at least
> STiH416 has an "ST proprietary multi-compartmental security IP and DRM
> processor".

You might be interested in the latest incarnation of the set.

See if it solves your issues.

https://lkml.org/lkml/2015/4/1/267

-- 
Lee Jones
Linaro STMicroelectronics Landing Team Lead
Linaro.org │ Open source software for ARM SoCs
Follow Linaro: Facebook | Twitter | Blog

      reply	other threads:[~2015-04-02 10:48 UTC|newest]

Thread overview: 21+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-02-24 17:33 Lee Jones
2015-02-24 17:33 ` [PATCH v3 1/4] ARM: sti: stih407-family: Supply defines for CLOCKGEN A0 Lee Jones
2015-02-24 17:33 ` [PATCH v3 2/4] ARM: sti: stih407-family: Add platform interconnects to always-on clk domain Lee Jones
2015-02-24 17:33 ` [PATCH v3 3/4] clk: Provide an always-on clock domain framework Lee Jones
2015-02-24 17:33 ` [PATCH v3 4/4] clk: dt: Introduce always-on clock domain documentation Lee Jones
2015-02-24 17:42 ` [PATCH v3 0/4] clk: st: New always-on clock domain Lee Jones
2015-02-27 21:37 ` Robert Jarzmik
2015-02-27 21:49   ` Lee Jones
2015-02-27 23:38     ` Robert Jarzmik
2015-03-02  8:30       ` Lee Jones
2015-03-02 11:29         ` Robert Jarzmik
2015-03-02 11:37           ` Lee Jones
2015-03-04 12:00 ` Lee Jones
2015-03-06 19:08   ` Mike Turquette
2015-03-09  9:28     ` Lee Jones
2015-03-25  4:11       ` Geert Uytterhoeven
2015-03-26 13:51         ` Lee Jones
2015-03-26 16:55           ` Geert Uytterhoeven
2015-03-26 19:38             ` Lee Jones
2015-04-02  8:31               ` Geert Uytterhoeven
2015-04-02 10:48                 ` Lee Jones [this message]

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