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

[Asutosh Das (asd)]

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@xxxxxxxxxxxxxx>
> > ---
> >   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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