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

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Date:   Wed, 25 Mar 2020 13:11:45 +0000
From:   Avri Altman <Avri.Altman@....com>
To:     Asutosh Das <asutoshd@...eaurora.org>,
        "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

> 
> 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?

>         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 ?

> +       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?


Thanks,
Avri