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Date:   Thu, 23 Jan 2020 15:50:01 +0800
From:   hongwus@codeaurora.org
To:     Can Guo <cang@codeaurora.org>
Cc:     asutoshd@codeaurora.org, nguyenb@codeaurora.org,
        rnayak@codeaurora.org, linux-scsi@vger.kernel.org,
        kernel-team@android.com, saravanak@google.com, salyzyn@google.com,
        Alim Akhtar <alim.akhtar@samsung.com>,
        Avri Altman <avri.altman@wdc.com>,
        Pedro Sousa <pedrom.sousa@synopsys.com>,
        "James E.J. Bottomley" <jejb@linux.ibm.com>,
        "Martin K. Petersen" <martin.petersen@oracle.com>,
        Stanley Chu <stanley.chu@mediatek.com>,
        Venkat Gopalakrishnan <venkatg@codeaurora.org>,
        Tomas Winkler <tomas.winkler@intel.com>,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH v4 2/8] scsi: ufs: set load before setting voltage in
 regulators
In-Reply-To: <1579764349-15578-3-git-send-email-cang@codeaurora.org>
References: <1579764349-15578-1-git-send-email-cang@codeaurora.org>
 <1579764349-15578-3-git-send-email-cang@codeaurora.org>
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Hi Can,
   It makes sense that set the load before enable regulator or set 
voltage. Just avoid voltage drop.

On 2020-01-23 15:25, Can Guo wrote:
> From: Asutosh Das <asutoshd@codeaurora.org>
> 
> This sequence change is required to avoid dips in voltage
> during boot-up.
> 
> Apparently, this dip is caused because in the original
> sequence, the regulators are initialized in lpm mode.
> And then when the load is set to high, and more current
> is drawn, than is allowed in lpm, the dip is seen.
> 
> Signed-off-by: Asutosh Das <asutoshd@codeaurora.org>
> Signed-off-by: Can Guo <cang@codeaurora.org>
> ---
>  drivers/scsi/ufs/ufshcd.c | 10 +++++-----
>  1 file changed, 5 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/scsi/ufs/ufshcd.c b/drivers/scsi/ufs/ufshcd.c
> index c2de29f..c386c2d 100644
> --- a/drivers/scsi/ufs/ufshcd.c
> +++ b/drivers/scsi/ufs/ufshcd.c
> @@ -7225,6 +7225,11 @@ static int ufshcd_config_vreg(struct device 
> *dev,
>  	name = vreg->name;
> 
>  	if (regulator_count_voltages(reg) > 0) {
> +		uA_load = on ? vreg->max_uA : 0;
> +		ret = ufshcd_config_vreg_load(dev, vreg, uA_load);
> +		if (ret)
> +			goto out;
> +
>  		if (vreg->min_uV && vreg->max_uV) {
>  			min_uV = on ? vreg->min_uV : 0;
>  			ret = regulator_set_voltage(reg, min_uV, vreg->max_uV);
> @@ -7235,11 +7240,6 @@ static int ufshcd_config_vreg(struct device 
> *dev,
>  				goto out;
>  			}
>  		}
> -
> -		uA_load = on ? vreg->max_uA : 0;
> -		ret = ufshcd_config_vreg_load(dev, vreg, uA_load);
> -		if (ret)
> -			goto out;
>  	}
>  out:
>  	return ret;


Reviewed-by: Hongwu Su <hongwus@codeaurora.org>