linux-kernel - Re: [PATCH 01/21] opp: Manage empty OPP tables with clk handle

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Date:   Mon, 13 Apr 2020 16:04:02 +0530
From:   Rajendra Nayak <rnayak@...eaurora.org>
To:     Viresh Kumar <viresh.kumar@...aro.org>
Cc:     sboyd@...nel.org, bjorn.andersson@...aro.org, agross@...nel.org,
        linux-arm-msm@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 01/21] opp: Manage empty OPP tables with clk handle


On 4/9/2020 1:27 PM, Viresh Kumar wrote:
> On 08-04-20, 19:16, Rajendra Nayak wrote:
>> With OPP core now supporting DVFS for IO devices, we have instances of
>> IO devices (same IP block) which require an OPP on some platforms/SoCs
> 
> By OPP you mean both freq and voltage here ?

yes, freq and perf state.

> 
>> while just needing to scale the clock on some others.
> 
> And only freq here ?

yes.

> 
>> In order to avoid conditional code in every driver which supports such
>> devices (to check for availability of OPPs and then deciding to do
>> either dev_pm_opp_set_rate() or clk_set_rate()) add support to manage
>> empty OPP tables with a clk handle.
> 
> Why can't these devices have an opp table with just rate mentioned in each node
> ?

These are existing devices already upstream.

> 
>> This makes dev_pm_opp_set_rate() equivalent of a clk_set_rate() for
>> devices with just a clk and no OPPs specified, and makes
>> dev_pm_opp_set_rate(0) bail out without throwing an error.
>>
>> Signed-off-by: Rajendra Nayak <rnayak@...eaurora.org>
>> ---
>>   drivers/opp/core.c | 14 ++++++++++++++
>>   1 file changed, 14 insertions(+)
>>
>> diff --git a/drivers/opp/core.c b/drivers/opp/core.c
>> index ba43e6a..e4f01e7 100644
>> --- a/drivers/opp/core.c
>> +++ b/drivers/opp/core.c
>> @@ -819,6 +819,8 @@ int dev_pm_opp_set_rate(struct device *dev, unsigned long target_freq)
>>   	if (unlikely(!target_freq)) {
>>   		if (opp_table->required_opp_tables) {
>>   			ret = _set_required_opps(dev, opp_table, NULL);
>> +		} else if (!_get_opp_count(opp_table)) {
>> +			return 0;
> 
> Why should anyone call this with target_freq = 0 ? I know it was required to
> drop votes in the above case, but why here ?

Well, it is to drop votes. But in cases where we don't have perf votes being put
(and only clock is scaled), the driver would still call this with freq = 0, i am
just making sure that in such cases its treated as a nop.

> 
>>   		} else {
>>   			dev_err(dev, "target frequency can't be 0\n");
>>   			ret = -EINVAL;
>> @@ -849,6 +851,18 @@ int dev_pm_opp_set_rate(struct device *dev, unsigned long target_freq)
>>   		goto put_opp_table;
>>   	}
>>   
>> +	/*
>> +	 * For IO devices which require an OPP on some platforms/SoCs
>> +	 * while just needing to scale the clock on some others
>> +	 * we look for empty OPP tables with just a clock handle and
>> +	 * scale only the clk. This makes dev_pm_opp_set_rate()
>> +	 * equivalent to a clk_set_rate()
>> +	 */
>> +	if (!_get_opp_count(opp_table)) {
>> +		ret = _generic_set_opp_clk_only(dev, clk, freq);
>> +		goto put_opp_table;
>> +	}
>> +
> 
> Is this enough? _of_add_opp_table_v2() returns with error if there is no OPP
> node within the table. Please give an example of how DT looks for the case you
> want to support.

FWIK, no one should call a _of_add_opp_table_v2 in cases where there is no OPP in DT?
The 'empty' OPP table from what I understand will be created by dev_pm_opp_set_clkname.
A good case to look at is the PATCH 13/21 in this series. The driver I am modifying
is used on sdm845/sc7180 and a host of other older qualcomm SoCs. Since i am adding
support for perf state voting using OPP only on sdm845/sc7180 I want the existing
platforms to just do what they were doing. Now thats not possible unless I start
adding a bunch of if/else around every opp call in the driver to distinguish between
the two.

I am a little surprised since I though the idea of doing something like this came from
you :) (or perhaps Stephen, I somehow can't recollect) to avoid all the if/else conditions
I had when I initially posted some of these changes.
Btw, you had this patch reviewed when this was posted a long while back too [1]

[1] https://patchwork.kernel.org/patch/11027217/

  
> 
>>   	temp_freq = old_freq;
>>   	old_opp = _find_freq_ceil(opp_table, &temp_freq);
>>   	if (IS_ERR(old_opp)) {
>> -- 
>> QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a member
>> of Code Aurora Forum, hosted by The Linux Foundation
> 

-- 
QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a member
of Code Aurora Forum, hosted by The Linux Foundation