Re: [PATCH 02/10 V4] omap3: pm: introduce opp accessor functions

[Nishanth Menon <nm@ti.com>]

Kevin Hilman had written, on 12/10/2009 05:25 PM, the following:
Thanks for the acks..

> Nishanth Menon <nm@ti.com> writes:
[...]

>> diff --git a/arch/arm/plat-omap/include/plat/opp.h b/arch/arm/plat-omap/include/plat/opp.h
>> new file mode 100644
>> index 0000000..341c02b

[...]

>> +/**
>> + * struct omap_opp - OMAP OPP description structure
>> + * @enabled: true/false - marking this OPP as enabled/disabled
>> + * @rate:    Frequency in hertz
>> + * @opp_id:  (DEPRECATED) opp identifier
>> + * @vsel:    Voltage in volt processor level(this usage is
>> + *           DEPRECATED to use Voltage in microvolts in future)
>> + *           uV = ((vsel * 12.5) + 600) * 1000
>> + *
>> + * This structure stores the OPP information for a given domain.
>> + * Due to legacy reasons, this structure is currently exposed and
>> + * will soon be removed elsewhere and will only be used as a handle
>> + * from the OPP internal referencing mechanism
>> + */
>> +struct omap_opp {
>> +     bool enabled;
>> +     unsigned long rate;
>> +     u8 opp_id __deprecated;
>> +     u16 vsel;
> 
> How about we add 'u32 voltage' here and mark vsel as __deprecated.  Then
> we no longer need both an 'struct omap_opp' and a 'struct omap_opp_def'.
> 
> Or even better, with the uv <--> vsel conversion macros you added,
> couldn't we alrady define the OPPs in terms of voltage, and drop the
> vsel already?

we should do that once we fix SR + resource34xx (underworks) - they 
directly use them and I kept my "status quo" rule switch on ;). Once it 
is done, vsel becomes voltage and an unsigned long. and we can manage it 
inside opp.c anyway we choose. For this starting set, I dont think we 
should do this.

[...]
> 
>> +/**
>> + * opp_find_freq_exact() - search for an exact frequency
>> + * @oppl:    OPP list
>> + * @freq:    frequency to search for
>> + * @enabled: enabled/disabled OPP to search for
>> + *
>> + * searches for the match in the opp list and returns handle to the matching
>> + * opp if found, else returns ERR_PTR in case of error and should be handled
>> + * using IS_ERR.
>> + *
>> + * Note enabled is a modifier for the search. if enabled=true, then the match is
>> + * for exact matching frequency and is enabled. if true, the match is for exact
>> + * frequency which is disabled.
>> + */
>> +struct omap_opp *opp_find_freq_exact(struct omap_opp *oppl,
>> +                                  unsigned long freq, bool enabled);
> 
> ack
> 
> I think we could drop the _exact, and just call it opp_find_freq(), but I'm
> ok either way.
shrug.. kinda matches with _approx .. it improves readability esp when 
people look at a usage code 6 months from now and question what 
find_freq is doing and get confused about freq_approx

[...]

>> +/**
>> + * struct omap_opp_def - OMAP OPP Definition
>> + * @enabled: True/false - is this OPP enabled/disabled by default
>> + * @freq:    Frequency in hertz corresponding to this OPP
>> + * @u_volt:  Nominal voltage in microvolts corresponding to this OPP
>> + *
>> + * OMAP SOCs have a standard set of tuples consisting of frequency and voltage
>> + * pairs that the device will support per voltage domain. This is called
>> + * Operating Points or OPP. The actual definitions of OMAP Operating Points
>> + * varies over silicon within the same family of devices. For a specific
>> + * domain, you can have a set of {frequency, voltage} pairs and this is denoted
>> + * by an array of omap_opp_def. As the kernel boots and more information is
>> + * available, a set of these are activated based on the precise nature of
>> + * device the kernel boots up on. It is interesting to remember that each IP
>> + * which belongs to a voltage domain may define their own set of OPPs on top
>> + * of this - but this is handled by the appropriate driver.
>> + */
>> +struct omap_opp_def {
>> +     bool enabled;
>> +     unsigned long freq;
>> +     u32 u_volt;
Comment to self: I should really make the u32 as unsigned long to be in 
sync with what is used elsewhere..(get_voltage)

>> +};
> 
> See above comment on 'struct omap_opp'.  I think these two should be
> combined.
> 
> I think the initial intent of having them separated so that the
> internal struct of 'struct omap_opp' could eventually move to the C
> file was the original intent, but I think it aids readability to just
> have a single OPP struct.

In a few weeks we wont have the struct omap_opp exposed out(once all the 
cleanups are done).. at that point, how would one define an OPP and 
expect to get an handle which they cannot manipulate?

> 
>> +/* Initialization wrapper */
>> +#define OMAP_OPP_DEF(_enabled, _freq, _uv)   \
>> +{                                            \
>> +     .enabled        = _enabled,             \
>> +     .freq           = _freq,                \
>> +     .u_volt         = _uv,                  \
>> +}
> 
> nice
> 
>> +/* Terminator for the initialization list */
>> +#define OMAP_OPP_DEF_TERMINATOR OMAP_OPP_DEF(0, 0, 0)
> 
> I'd just drop this and use OMAP_OPP_DEF(0, 0, 0) directly in
> the table.

Am ok with either (I dont like additional #defs). but terminator helps 
redability a bit though (debatable).. any reasons why u'd like it 0,0,0?
> 
>> +/**
>> + * opp_init_list() - Initialize an opp list from the opp definitions
>> + * @opp_defs:        Initial opp definitions to create the list.
>> + *
>> + * This function creates a list of opp definitions and returns a handle.
>> + * This list can be used to further validation/search/modifications. New
>> + * opp entries can be added to this list by using opp_add().
>> + *
>> + * In the case of error, ERR_PTR is returned to the caller and should be
>> + * appropriately handled with IS_ERR.
>> + */
>> +struct omap_opp __init *opp_init_list(const struct omap_opp_def *opp_defs);
> 
> My original suggestion was that opp_init_list() simply creates a new
> but empty list.  Adding OPPs should be done using opp_add().
> 
> I guess I'm OK with having the 'bulk add' feature of init_list() but
> would rather see a single way to add OPPs.
Reasons why to have a buld add feature in init:
a) There is opp_add below which allows u to add single opp
b) In terms of walk thru code duplication (once this gets used accross 
OMAPs) it is essentially the same thing we do (add each OPP definition 
for a domain)..
c) you dont incur function call latencies. (ok not a big deal.. but still).

> 
>> +/**
>> + * opp_add()  - Add an OPP table from a table definitions
>> + * @oppl:    List to add the OPP to
>> + * @opp_def: omap_opp_def to describe the OPP which we want to add to list.
>> + *
>> + * This function adds an opp definition to the opp list and returns
>> + * a handle representing the new OPP list. This handle is then used for further
>> + * validation, search, modification operations on the OPP list.
>> + *
>> + * This function returns the pointer to the allocated list through oppl if
>> + * success, else corresponding ERR_PTR value. Caller should NOT free the oppl.
>> + * opps_defs can be freed after use.
>> + *
>> + * NOTE: caller should assume that on success, oppl is probably populated with
>> + * a new handle and the new handle should be used for further referencing
>> + */
>> +struct omap_opp *opp_add(struct omap_opp *oppl,
>> +                      const struct omap_opp_def *opp_def);
> 
> c.f. proposal to drop omap_opp_def.
explained above.

> 
> otherwise, ack.
> 

-- 
Regards,
Nishanth Menon