[PATCH 2/3] ARM: OMAP2+: Add support to parse optional clk info from DT

[Mark Rutland]

On Wed, Aug 14, 2013 at 03:05:25PM +0100, Rajendra Nayak wrote:
> On Wednesday 14 August 2013 07:28 PM, Nishanth Menon wrote:
> > On 08/14/2013 08:49 AM, Mark Rutland wrote:
> >> [Adding Mike Turquette and dt maintainers]
> >>
> >> On Wed, Aug 14, 2013 at 02:39:44PM +0100, Nishanth Menon wrote:
> >>> On 08/14/2013 08:20 AM, Rajendra Nayak wrote:
> >>>> On Wednesday 14 August 2013 06:18 PM, Nishanth Menon wrote:
> >>>>> Hi Rajendra,
> >>>>>
> >>>>> On Tue, Jul 23, 2013 at 1:24 AM, Rajendra Nayak <rnayak at ti.com> wrote:
> >>>>> [..]
> >>>>>> diff --git a/arch/arm/mach-omap2/omap_hwmod.c b/arch/arm/mach-omap2/omap_hwmod.c
> >>>>>> index 12fa589..e5c804b 100644
> >>>>>> --- a/arch/arm/mach-omap2/omap_hwmod.c
> >>>>>> +++ b/arch/arm/mach-omap2/omap_hwmod.c
> >>>>>> @@ -805,6 +805,65 @@ static int _init_interface_clks(struct omap_hwmod *oh)
> >>>>>>           return ret;
> >>>>>>    }
> >>>>>>
> >>>>>> +static const char **_parse_opt_clks_dt(struct omap_hwmod *oh,
> >>>>>> +                                      struct device_node *np,
> >>>>>> +                                      int *opt_clks_cnt)
> >>>>>> +{
> >>>>>> +       int i, clks_cnt;
> >>>>>> +       const char *clk_name;
> >>>>>> +       const char **opt_clk_names;
> >>>>>> +
> >>>>>> +       clks_cnt = of_property_count_strings(np, "clock-names");
> >>>>>> +       if (!clks_cnt)
> >>>>>> +               return NULL;
> >>>>>> +
> >>>>>> +       opt_clk_names = kzalloc(sizeof(char *)*clks_cnt, GFP_KERNEL);
> >>>>>> +       if (!opt_clk_names)
> >>>>>> +               return NULL;
> >>>>>> +
> >>>>>> +       for (i = 0; i < clks_cnt; i++) {
> >>>>>> +               of_property_read_string_index(np, "clock-names", i, &clk_name);
> >>>>>> +               if (!strcmp(clk_name, "fck"))
> >>>>>
> >>>>> Could we instead parse for names that are "optional,role_name" instead
> >>>>> of assuming anything other than fck is optional clocks?
> >>>>
> >>>> you mean look for anything with optional,*? because the role names would change.
> >>>>
> >>>
> >>> yes. the idea being, we now have a meaning to the clock name - there are
> >>> two types of clocks here.. functional and optional, we *might* have
> >>> facility to add interface clock(we dont know interface clock handling
> >>> yet, but something in the future).. we might increase the support for
> >>> number of functional clocks.. it might help to keep the format such that
> >>> it is a "bit extendable".
> >>
> >> I completely disagree. The only things that should appear in clock-names
> >> are the names of the clock inputs that appear in the manual for the
> >> device. The driver should know which ones are optional, as that's a
> >> fixed property of the IP and the way the driver uses it.
> >>
> >> You should not be embedding additional semantics in name properties.
> > 
> > we use an level of abstraction called omap_device and hwmod to allow devices to use a generic pm_runtime. drivers for specific blocks dont normally need to know about the clocks to deal with. This allows maximum reuse consider concept is generic enough.
> 
> They do know about the optional clocks though and request and release them when needed. The need for hwmod to know about optional clocks
> (and enable all) arises from the fact that some of these devices need *some* optional clocks for a successful reset.
> And given hmwod has no knowledge about which optional ones (if at all) will be needed, it goes ahead and enables all before doing a reset.
> This is something done only at init time and *not* something thats done every time the device is enabled by the driver using pm_runtime.

To clarify:

I was initially confused as to the purpose of the code. I'm not against
a one-off clock initialisation to put everything into a sane state. If
we can't trust the bootloaders, that seems like a necessary evil. I'll
leave Mike to comment on whether and how that should be done.

I do not think we should be embedding clock semantics in clock-names.
That's not the way the property is intended to be used, it breaks
uniformity, and it's an abuse of the system that may come back to bite
us later.

Thanks,
Mark.