linux-kernel - Re: [PATCH v1 2/2] scsi: ufs: Support reading UFS's Vcc voltage from device tree

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Date:   Tue, 15 Sep 2020 08:46:38 -0500
From:   Bjorn Andersson <bjorn.andersson@...aro.org>
To:     "Bao D. Nguyen" <nguyenb@...eaurora.org>
Cc:     cang@...eaurora.org, asutoshd@...eaurora.org,
        martin.petersen@...cle.com, linux-scsi@...r.kernel.org,
        linux-arm-msm@...r.kernel.org,
        Alim Akhtar <alim.akhtar@...sung.com>,
        Avri Altman <avri.altman@....com>,
        "James E.J. Bottomley" <jejb@...ux.ibm.com>,
        YueHaibing <yuehaibing@...wei.com>,
        Bean Huo <beanhuo@...ron.com>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v1 2/2] scsi: ufs: Support reading UFS's Vcc voltage from
 device tree

On Tue 01 Sep 01:00 CDT 2020, Bao D. Nguyen wrote:

> The UFS specifications supports a range of Vcc operating voltage
> from 2.4-3.6V depending on the device and manufacturers.
> Allows selecting the UFS Vcc voltage level by setting the
> UFS's entry vcc-voltage-level in the device tree. If UFS's
> vcc-voltage-level setting is not found in the device tree,
> use default values provided by the driver.
> 

As stated in the reply to patch 1, this is not the right approach.  As
long as you have static min/max values requested by the driver you
should rely on the board's constraints for the regulator levels and
instead remove the min_uV/max_uV code from the driver.

Thanks,
Bjorn

> Signed-off-by: Can Guo <cang@...eaurora.org>
> Signed-off-by: Asutosh Das <asutoshd@...eaurora.org>
> Signed-off-by: Bao D. Nguyen <nguyenb@...eaurora.org>
> ---
>  drivers/scsi/ufs/ufshcd-pltfrm.c | 15 ++++++++++++---
>  1 file changed, 12 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/scsi/ufs/ufshcd-pltfrm.c b/drivers/scsi/ufs/ufshcd-pltfrm.c
> index 3db0af6..48f429c 100644
> --- a/drivers/scsi/ufs/ufshcd-pltfrm.c
> +++ b/drivers/scsi/ufs/ufshcd-pltfrm.c
> @@ -104,10 +104,11 @@ static int ufshcd_parse_clock_info(struct ufs_hba *hba)
>  static int ufshcd_populate_vreg(struct device *dev, const char *name,
>  		struct ufs_vreg **out_vreg)
>  {
> -	int ret = 0;
> +	int len, ret = 0;
>  	char prop_name[MAX_PROP_SIZE];
>  	struct ufs_vreg *vreg = NULL;
>  	struct device_node *np = dev->of_node;
> +	const __be32 *prop;
>  
>  	if (!np) {
>  		dev_err(dev, "%s: non DT initialization\n", __func__);
> @@ -138,8 +139,16 @@ static int ufshcd_populate_vreg(struct device *dev, const char *name,
>  			vreg->min_uV = UFS_VREG_VCC_1P8_MIN_UV;
>  			vreg->max_uV = UFS_VREG_VCC_1P8_MAX_UV;
>  		} else {
> -			vreg->min_uV = UFS_VREG_VCC_MIN_UV;
> -			vreg->max_uV = UFS_VREG_VCC_MAX_UV;
> +			prop = of_get_property(np, "vcc-voltage-level", &len);
> +			if (!prop || (len != (2 * sizeof(__be32)))) {
> +				dev_warn(dev, "%s vcc-voltage-level property.\n",
> +					prop ? "invalid format" : "no");
> +				vreg->min_uV = UFS_VREG_VCC_MIN_UV;
> +				vreg->max_uV = UFS_VREG_VCC_MAX_UV;
> +			} else {
> +				vreg->min_uV = be32_to_cpup(&prop[0]);
> +				vreg->max_uV = be32_to_cpup(&prop[1]);
> +			}
>  		}
>  	} else if (!strcmp(name, "vccq")) {
>  		vreg->min_uV = UFS_VREG_VCCQ_MIN_UV;
> -- 
> The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
> a Linux Foundation Collaborative Project
>