Re: [PATCH 1/3] PM / devfreq: Actually support providing freq_table
From: Chanwoo Choi
Date: Tue Apr 24 2018 - 03:26:33 EST
On 2018ë 04ì 24ì 14:29, Bjorn Andersson wrote:
> On Mon 23 Apr 19:48 PDT 2018, Chanwoo Choi wrote:
>> On 2018??? 04??? 24??? 09:20, Bjorn Andersson wrote:
>>> The code in devfreq_add_device() handles the case where a freq_table is
>>> passed by the client, but then requests min and max frequences from
>>> the, in this case absent, opp tables.
>>> Read the min and max frequencies from the frequency table, which has
>>> been built from the opp table if one exists, instead of querying the
>>> opp table.
>>> Signed-off-by: Bjorn Andersson <bjorn.andersson@xxxxxxxxxx>
>>> An alternative approach is to clarify in the devfreq code that it's not
>>> possible to pass a freq_table and then in patch 3 create an opp table for the
>>> device in runtime; although the error handling of this becomes non-trivial.
>>> Transitioning the UFSHCD to use opp tables directly is hindered by the fact
>>> that the Qualcomm UFS hardware has two different clocks that needs to be
>>> running at different rates, so we would need a way to describe the two rates in
>>> the opp table. (And would force us to change the DT binding)
>>> drivers/devfreq/devfreq.c | 22 ++++------------------
>>> 1 file changed, 4 insertions(+), 18 deletions(-)
>>> diff --git a/drivers/devfreq/devfreq.c b/drivers/devfreq/devfreq.c
>>> index fe2af6aa88fc..086ced50a13d 100644
>>> --- a/drivers/devfreq/devfreq.c
>>> +++ b/drivers/devfreq/devfreq.c
>>> @@ -74,30 +74,16 @@ static struct devfreq *find_device_devfreq(struct device *dev)
>>> static unsigned long find_available_min_freq(struct devfreq *devfreq)
>>> - struct dev_pm_opp *opp;
>>> - unsigned long min_freq = 0;
>>> - opp = dev_pm_opp_find_freq_ceil(devfreq->dev.parent, &min_freq);
>>> - if (IS_ERR(opp))
>>> - min_freq = 0;
>>> - else
>>> - dev_pm_opp_put(opp);
>>> + struct devfreq_dev_profile *profile = devfreq->profile;
>>> - return min_freq;
>>> + return profile->freq_table;
>> It is wrong. The thermal framework support the devfreq-cooling device
>> which uses the dev_pm_opp_enable/disable().
> Okay, that makes sense. So rather than registering a custom freq_table I
> should register the min and max frequency using dev_pm_opp_add().
>> In order to find the correct available min frequency,
>> the devfreq have to use the OPP function instead of using the first entry
>> of the freq_table array.
> Based on this there seems to be room for cleaning out the freq_table
> from devfreq, to reduce the confusion. I will review this further.
Actually, devfreq must need to have the freq_table array. But, freq_table
array should be handled in the devfreq core. Now, the devfreq device drivers can
touch the freq_table. I think it is not good.
There is a reason why we have to maintain the freq_table as the internal variable.
OPP doesn't provide the OPP API which get the all registered frequencies.
If devfreq-cooling device disables the specific frequency by using dev_pm_oppdisable(),
the user of OPP interface can not get the disabled frequency list.
So, I maintain the freq_table even if using the OPP interface.
And, devfreq-cooling device uses the freq_table directly because released MALi driver
from ARM initializes the freq_table list directly.
I have no any objection for refactoring. Just I'm sharing the issue and current status.