linux-kernel - Re: [PATCH v1 1/2] scsi: ufs: add required delay after gating reference clock

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Date:   Mon, 17 Feb 2020 20:58:20 +0800
From:   Can Guo <cang@...eaurora.org>
To:     Stanley Chu <stanley.chu@...iatek.com>
Cc:     linux-scsi@...r.kernel.org, martin.petersen@...cle.com,
        avri.altman@....com, alim.akhtar@...sung.com, jejb@...ux.ibm.com,
        beanhuo@...ron.com, asutoshd@...eaurora.org,
        matthias.bgg@...il.com, bvanassche@....org,
        linux-mediatek@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        kuohong.wang@...iatek.com, peter.wang@...iatek.com,
        chun-hung.wu@...iatek.com, andy.teng@...iatek.com
Subject: Re: [PATCH v1 1/2] scsi: ufs: add required delay after gating
 reference clock

On 2020-02-17 17:35, Stanley Chu wrote:
> In UFS version 3.0, a newly added attribute bRefClkGatingWaitTime 
> defines
> the minimum time for which the reference clock is required by device 
> during
> transition to LS-MODE or HIBERN8 state.
> 
> Currently this time is detected and stored in
> hba->dev_info.clk_gating_wait_us but applied to vendor implementatios 
> only.
> Make it applied to reference clock named as "ref_clk" in device tree in
> common path.
> 
> Signed-off-by: Stanley Chu <stanley.chu@...iatek.com>
> ---
>  drivers/scsi/ufs/ufshcd.c | 8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/scsi/ufs/ufshcd.c b/drivers/scsi/ufs/ufshcd.c
> index 744b8254220c..7f60721f54d1 100644
> --- a/drivers/scsi/ufs/ufshcd.c
> +++ b/drivers/scsi/ufs/ufshcd.c
> @@ -7417,8 +7417,10 @@ static int __ufshcd_setup_clocks(struct ufs_hba
> *hba, bool on,
>  	struct ufs_clk_info *clki;
>  	struct list_head *head = &hba->clk_list_head;
>  	unsigned long flags;
> +	unsigned long wait_us;
>  	ktime_t start = ktime_get();
>  	bool clk_state_changed = false;
> +	bool ref_clk;
> 
>  	if (list_empty(head))
>  		goto out;
> @@ -7436,7 +7438,8 @@ static int __ufshcd_setup_clocks(struct ufs_hba
> *hba, bool on,
> 
>  	list_for_each_entry(clki, head, list) {
>  		if (!IS_ERR_OR_NULL(clki->clk)) {
> -			if (skip_ref_clk && !strcmp(clki->name, "ref_clk"))
> +			ref_clk = !strcmp(clki->name, "ref_clk") ? true : false;
> +			if (skip_ref_clk && ref_clk)
>  				continue;
> 
>  			clk_state_changed = on ^ clki->enabled;
> @@ -7449,6 +7452,9 @@ static int __ufshcd_setup_clocks(struct ufs_hba
> *hba, bool on,
>  				}
>  			} else if (!on && clki->enabled) {
>  				clk_disable_unprepare(clki->clk);
> +				wait_us = hba->dev_info.clk_gating_wait_us;
> +				if (ref_clk && wait_us)
> +					usleep_range(wait_us, wait_us + 10);

Hi Stanley,

If wait_us is 1us, it would be inappropriate to use usleep_range() here.
You have checks of the delay in patch #2, but why it is not needed here?

Thanks,
Can Guo.

>  			}
>  			clki->enabled = on;
>  			dev_dbg(hba->dev, "%s: clk: %s %sabled\n", __func__,