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

From: [email-masked] (Rajendra Nayak)
Date: Wed, 14 Aug 2013 19:38:43 +0530

On Wednesday 14 August 2013 07:35 PM, 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 <[email-masked]> 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.

We do seem to have a flag 'HWMOD_CONTROL_OPT_CLKS_IN_RESET' which says which ones really need optional clocks to be controlled.
I guess for the rest hwmod can even ignore optional clocks completely.

> 
>>
>> The traditional way of dealing with this has been to encode the *names* *inside* hwmod!!! which is obviously the wrong way to deal with with clock nodes in dts.
>>
>> This series moves away from that approach - which is good. Now, the question is:
>>
>> clocks-names = "....."  is not sufficient to indicate a list of clocks of different functions
>>
>> 3 types of clocks may exist for OMAP h/w blocks:
>> a) functional clock (1 usually, but we are starting to see multiple fclks). this drives the actual functionality
>> b) optional clocks - additional clocks such as debounce clock etc. - there can be n such clocks
>> c) interface clocks - this drives the register interface on the bus.  - there can be n such clocks and additional headaches for interface - currently embedded inside hwmod.
>>
>> you could do:
>> A) embedd in the sematics of the name
>> clock-names="fck", "optional,role1",  "optional,role2";
>> clocks= <&clk_a>, <&clk_x>, <&clk_y>;
>> OR:
>> B) embedd in the property name
>> optional-clock-names="optional,role1",  "optional,role2";
>> optional-clocks=<&clk_x>, <&clk_y>;
>> functional-clock-names="fck";
>> functional-clocks=<&clk_a>;
>>
>> are you suggesting (b) here?
>>
>