Re: [STLinux Kernel] [PATCH 3/4] clk: Provide always-on clock support

[Maxime Coquelin]

On 03/02/2015 11:18 AM, Lee Jones wrote:
> On Mon, 02 Mar 2015, Jassi Brar wrote:
>
> > On Mon, Mar 2, 2015 at 2:06 PM, Lee Jones <lee.jones@xxxxxxxxxx> wrote:
> > > On Sat, 28 Feb 2015, Jassi Brar wrote:
> > >
> > > > On 28 February 2015 at 02:44, Lee Jones <lee.jones@xxxxxxxxxx> wrote:
> > > > > Lots of platforms contain clocks which if turned off would prove fatal.
> > > > > The only way to recover from these catastrophic failures is to restart
> > > > > the board(s).  Now, when a clock is registered with the framework it is
> > > > > compared against a list of provided always-on clock names which must be
> > > > > kept ungated.  If it matches, we enable the existing CLK_IGNORE_UNUSED
> > > > > flag, which will prevent the common clk framework from attempting to
> > > > > gate it during the clk_disable_unused() procedure.
> > > > If a clock is critical on a certain board, it could be got+enabled
> > > > during early boot so there is always a user.
> > > I tried this.  There was push-back from the DT maintainers.
> > >
> > >    http://lists.infradead.org/pipermail/linux-arm-kernel/2015-February/324417.html
> > Thanks, I wasn't aware of the history.
> >
> > > > To be able to do that from DT, maybe add a new, say, CLK_ALWAYS_ON
> > > > flag could be made to initialize the clock with one phantom user
> > > > already. Or just reuse the CLK_IGNORE_UNUSED?
> > > How is that different to what this set is doing?
> > The phantom user - that's there but none can see it.
> >
> > How about?
> >
> > +       of_property_for_each_string(np, "clock-always-on", prop, clkname) {
> > +               clk = __clk_lookup(clkname);
> > +               if (!clk)
> > +                       continue;
> > +
> > +               clk->core->enable_count = 1;
> > +               clk->core->prepare_count = 1;
> > +       }
> This is only fractionally different from the current implementation.
>
> I believe the current way it slightly nicer, as we don't have to fake
> the user count.  This solution is saying "one of the drivers is still
> consuming this clock", instead, in the original implementation we're
> saying "we know there are no consumers of this clock, but keep it on
> anyway due to [insert reason here]".
So maybe introducing a new "CLK_DISABLE_NEVER" flag will be more
explicit than hacking around "CLK_IGNORE_UNUSED" one?

BR,
Maxime
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