Re: [PATCH] opp: introduce library for device-specific OPPs

Nishanth Menon
2010-09-17T15:30:19Z

Aguirre, Sergio had written, on 09/17/2010 09:09 AM, the following:
> Hi Nishanth,
thanks for the review.. comments below..

[...]
>> diff --git a/include/linux/opp.h b/include/linux/opp.h
>> new file mode 100644
>> index 0000000..94a552b
>> --- /dev/null
>> +++ b/include/linux/opp.h
>> @@ -0,0 +1,136 @@
>> +/*
>> + * Generic OPP Interface
>> + *
>> + * Copyright (C) 2009-2010 Texas Instruments Incorporated.
>> + * Nishanth Menon
>> + * Romit Dasgupta <romit@ti.com>
>> + * Copyright (C) 2009 Deep Root Systems, LLC.
>> + * Kevin Hilman
>
> Just curious why only Romit's e-mail address is there, and not Kevin's or
> yours...

personal choice I guess, Romit prefered his email id added Kevin and I
did not.

[...]

>> diff --git a/lib/opp.c b/lib/opp.c
>> new file mode 100644
>> index 0000000..650c8c3
>> --- /dev/null
>> +++ b/lib/opp.c
>> @@ -0,0 +1,440 @@
>> +/*
>> + * Generic OPP Interface
[...]
>> +
>> +/**
>> + * struct device_opp - Device opp structure
>> + * @node: list node
>> + * @dev: device handle
>> + * @opp_list: list of opps
>> + * @opp_count: num opps
>> + * @enabled_opp_count: how many opps are actually enabled
>> + *
>> + * This is an internal datastructure maintaining the link to
>> + * opps attached to a domain device. This structure is not
>> + * meant to be shared with users as it private to opp layer.
>
> "... as it is private ..."
thanks. will fix.
[..]
>> +/**
>> + * opp_get_voltage() - Gets the voltage corresponding to an opp
>> + * @opp: opp for which voltage has to be returned for
>> + *
>> + * Return voltage in micro volt corresponding to the opp, else
>> + * return 0
>> + */
>> +unsigned long opp_get_voltage(const struct opp *opp)
>> +{
>> + if (unlikely(!opp || IS_ERR(opp)) || !opp->enabled) {
>> + pr_err("%s: Invalid parameters being passed\n", __func__);
>> + return 0;
>
> Shouldn't the case for !opp->enabled just return 0, without error reporting.
>
> IMHO, having an OPP disabled is not really a bug in params, and returning this, will misinform the user.. I think.
>
> What do you think?

I think we discussed it a little earlier in the chain
http://marc.info/?t=128152609200064&r=1&w=2
the operations of get_freq and get_voltage dont make sense to be used on
a disabled OPP. if we are using it so, we need to report an error to the
user and log it for debugging.

The intent is as follows:
a) find_freq_exact is the function to use for finding the opp which is
disabled (without the opp pointer, you cant query voltage and frequency
anyways).
b) to query this, you need to know the opp frequency anyways, so it
makes no usage sense for get_freq or get_voltage to be able to be using
a disabled opp.

Do we think it makes sense to add this info to the documentation as well?

>
>> + }
>> +
>> + return opp->u_volt;
>> +}
>> +
>> +/**
>> + * opp_get_freq() - Gets the frequency corresponding to an opp
>> + * @opp: opp for which frequency has to be returned for
>> + *
>> + * Return frequency in hertz corresponding to the opp, else
>> + * return 0
>> + */
>> +unsigned long opp_get_freq(const struct opp *opp)
>> +{
>> + if (unlikely(!opp || IS_ERR(opp)) || !opp->enabled) {
>> + pr_err("%s: Invalid parameters being passed\n", __func__);
>> + return 0;
>
> Similarly here.
commented above.

>
>> + }
>> +
>> + return opp->rate;
>> +}
>> +
>> +/**
>> + * opp_get_opp_count() - Get number of opps enabled in the opp list
>> + * @dev: device for which we do this operation
>> + *
>> + * This functions returns the number of opps if there are any OPPs
>
> "This function returns.."
Thanks. will fix in v2 post.

>
>> enabled,
>> + * else returns corresponding error value.
>> + */
>> +int opp_get_opp_count(struct device *dev)
>> +{
>> + struct device_opp *dev_opp;
>> +
>> + dev_opp = find_device_opp(dev);
>> + if (IS_ERR(dev_opp))
>> + return -ENODEV;
>> +
>> + return dev_opp->enabled_opp_count;
>> +}
>> +
>> +/**
>> + * opp_find_freq_exact() - search for an exact frequency
>> + * @dev: device for which we do this operation
>> + * @freq: frequency to search for
>> + * @enabled: enabled/disabled OPP to search for
>> + *
>> + * Searches for exact 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 false, the match is
>> for
>> + * exact frequency which is disabled.
>
> That enabled var is ignored, which makes this explanation mismatch with the code behavior.
>
> Am I missing something?
ouch.. you are correct.. it is a mistake that got introduced in one of
the merges we did.. the matching check
if (temp_opp->enabled && temp_opp->rate == freq) {
should have been
if (temp_opp->enabled == enabled && temp_opp->rate == freq) {

Thanks for catching it.

>
>> + */
>> +struct opp *opp_find_freq_exact(struct device *dev,
>> + unsigned long freq, bool enabled)
>> +{
>> + struct device_opp *dev_opp;
>> + struct opp *temp_opp, *opp = ERR_PTR(-ENODEV);
>> +
>> + dev_opp = find_device_opp(dev);
>> + if (IS_ERR(dev_opp))
>> + return opp;
>> +
>> + list_for_each_entry(temp_opp, &dev_opp->opp_list, node) {
>> + if (temp_opp->enabled && temp_opp->rate == freq) {
>> + opp = temp_opp;
>> + break;
>> + }
>> + }
>> +
>> + return opp;
>> +}
>> +
>> +/**
>> + * opp_find_freq_ceil() - Search for an rounded ceil freq
>> + * @dev: device for which we do this operation
>> + * @freq: Start frequency
>> + *
>> + * Search for the matching ceil *enabled* OPP from a starting freq
>> + * for a domain.
>> + *
>> + * Returns *opp and *freq is populated with the match, else
>> + * returns NULL opp if no match, else returns ERR_PTR in case of error.
>
> By looking at the code below, I don't think returning NULL is a possibility.
yet another documentation error.. thanks for catching.
ERR_PTR(-ENODEV) is returned instead of NULL..

how about "
Returns *opp and *freq is populated with the match if found, else
returns ERR_PTR in case of error and should be handled using IS_ERR.

"
>
>> + *
>> + * Example usages:
>> + * * find match/next highest available frequency *
>> + * freq = 350000;
>> + * opp = opp_find_freq_ceil(dev, &freq))
>> + * if (IS_ERR(opp))
>> + * pr_err("unable to find a higher frequency\n");
>> + * else
>> + * pr_info("match freq = %ld\n", freq);
>> + *
>> + * * print all supported frequencies in ascending order *
>> + * freq = 0; * Search for the lowest enabled frequency *
>> + * while (!IS_ERR(opp = opp_find_freq_ceil(OPP_MPU, &freq)) {
>> + * pr_info("freq = %ld\n", freq);
>> + * freq++; * for next higher match *
>> + * }
>> + */
>> +struct opp *opp_find_freq_ceil(struct device *dev, unsigned long *freq)
>> +{
>> + struct device_opp *dev_opp;
>> + struct opp *temp_opp, *opp = ERR_PTR(-ENODEV);
>> +
>> + dev_opp = find_device_opp(dev);
>> + if (IS_ERR(dev_opp))
>> + return opp;
>> +
>> + list_for_each_entry(temp_opp, &dev_opp->opp_list, node) {
>> + if (temp_opp->enabled && temp_opp->rate >= *freq) {
>
> What if freq contains a NULL pointer?
thanks.. good catch.. should have checked for dev and freq on entry..
added in the to be posted v2

>
>> + opp = temp_opp;
>> + *freq = opp->rate;
>> + break;
>> + }
>> + }
>> +
>> + return opp;
>> +}
>> +
>> +/**
>> + * opp_find_freq_floor() - Search for an rounded floor freq
>
> "... Search for a rounded floor ..."
Thanks.. will fix in v2.

>
>> + * @dev: device for which we do this operation
>> + * @freq: Start frequency
>> + *
>> + * Search for the matching floor *enabled* OPP from a starting freq
>> + * for a domain.
>> + *
>> + * Returns *opp and *freq is populated with the next match, else
>> + * returns NULL opp if no match, else returns ERR_PTR in case of error.
>
> Similar comment about opp not being ever NULL as the function above.

Suggest replacing with:
Returns *opp and *freq is populated with the match if found, else
returns ERR_PTR in case of error and should be handled using IS_ERR.

[..]

--
Regards,
Nishanth Menon