linux-kernel - Re: [PATCH v1 1/3] scsi: ufshcd: Update the set frequency to devfreq

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Date:   Wed, 25 Mar 2020 09:32:24 -0700
From:   "Asutosh Das (asd)" <asutoshd@...eaurora.org>
To:     Avri Altman <Avri.Altman@....com>,
        "cang@...eaurora.org" <cang@...eaurora.org>,
        "martin.petersen@...cle.com" <martin.petersen@...cle.com>,
        "linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>
Cc:     "linux-arm-msm@...r.kernel.org" <linux-arm-msm@...r.kernel.org>,
        Alim Akhtar <alim.akhtar@...sung.com>,
        "James E.J. Bottomley" <jejb@...ux.ibm.com>,
        Stanley Chu <stanley.chu@...iatek.com>,
        Bean Huo <beanhuo@...ron.com>,
        Bart Van Assche <bvanassche@....org>,
        Venkat Gopalakrishnan <venkatg@...eaurora.org>,
        Tomas Winkler <tomas.winkler@...el.com>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v1 1/3] scsi: ufshcd: Update the set frequency to devfreq

On 3/25/2020 6:11 AM, Avri Altman wrote:
>>
>> Currently, the frequency that devfreq provides the
>> driver to set always leads the clocks to be scaled up.
>> Hence, round the clock-rate to the nearest frequency
>> before deciding to scale.
>>
>> Also update the devfreq statistics of current frequency.
>>
>> Signed-off-by: Asutosh Das <asutoshd@...eaurora.org>
>> ---
>>   drivers/scsi/ufs/ufshcd.c | 14 +++++++++++++-
>>   1 file changed, 13 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/scsi/ufs/ufshcd.c b/drivers/scsi/ufs/ufshcd.c
>> index 2a2a63b..4607bc6 100644
>> --- a/drivers/scsi/ufs/ufshcd.c
>> +++ b/drivers/scsi/ufs/ufshcd.c
>> @@ -1187,6 +1187,9 @@ static int ufshcd_devfreq_target(struct device
>> *dev,
>>          if (!ufshcd_is_clkscaling_supported(hba))
>>                  return -EINVAL;
>>
>> +       clki = list_first_entry(&hba->clk_list_head, struct ufs_clk_info, list);
>> +       /* Override with the closest supported frequency */
>> +       *freq = (unsigned long) clk_round_rate(clki->clk, *freq);
>>          spin_lock_irqsave(hba->host->host_lock, irq_flags);
> Please remind me what the spin lock is protecting here?

Hmmm ... Nothing comes to my mind. I blamed it but it's a part of a 
bigger change.

> 
>>          if (ufshcd_eh_in_progress(hba)) {
>>                  spin_unlock_irqrestore(hba->host->host_lock, irq_flags);
>> @@ -1201,8 +1204,13 @@ static int ufshcd_devfreq_target(struct device
>> *dev,
>>                  goto out;
>>          }
>>
>> -       clki = list_first_entry(&hba->clk_list_head, struct ufs_clk_info, list);
>> +       /* Decide based on the rounded-off frequency and update */
>>          scale_up = (*freq == clki->max_freq) ? true : false;
>> +       if (scale_up)
>> +               *freq = clki->max_freq;
> This was already established 2 lines above ?
Good point - I'll change it.

> 
>> +       else
>> +               *freq = clki->min_freq;
>> +       /* Update the frequency */
>>          if (!ufshcd_is_devfreq_scaling_required(hba, scale_up)) {
>>                  spin_unlock_irqrestore(hba->host->host_lock, irq_flags);
>>                  ret = 0;
>> @@ -1250,6 +1258,8 @@ static int ufshcd_devfreq_get_dev_status(struct
>> device *dev,
>>          struct ufs_hba *hba = dev_get_drvdata(dev);
>>          struct ufs_clk_scaling *scaling = &hba->clk_scaling;
>>          unsigned long flags;
>> +       struct list_head *clk_list = &hba->clk_list_head;
>> +       struct ufs_clk_info *clki;
>>
>>          if (!ufshcd_is_clkscaling_supported(hba))
>>                  return -EINVAL;
>> @@ -1260,6 +1270,8 @@ static int ufshcd_devfreq_get_dev_status(struct
>> device *dev,
>>          if (!scaling->window_start_t)
>>                  goto start_window;
>>
>> +       clki = list_first_entry(clk_list, struct ufs_clk_info, list);
>> +       stat->current_frequency = clki->curr_freq;
> Is this a bug fix? > devfreq_simple_ondemand_func is trying to establish the busy period,
> but also uses the frequency in its calculation - which I wasn't able to understand how.
> Can you add a short comment why updating current_frequency is needed?
>
Sure - I'll add a comment. If stat->current_frequency is not updated, 
the governor would always ask to set the max freq because the initial 
frequency was unknown to it. Reference - devfreq_simple_ondemand_func(...)

> 
> Thanks,
> Avri
> 

Thanks,
-asd

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