linux-kernel - Re: [RFC PATCH v1] scsi: ufs: Remove pre-defined initial VCC voltage values

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Date:   Mon, 30 Nov 2020 17:09:32 -0600
From:   Bjorn Andersson <bjorn.andersson@...aro.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, cang@...eaurora.org,
        matthias.bgg@...il.com, bvanassche@....org,
        linux-mediatek@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        nguyenb@...eaurora.org, kuohong.wang@...iatek.com,
        peter.wang@...iatek.com, chun-hung.wu@...iatek.com,
        andy.teng@...iatek.com, chaotian.jing@...iatek.com,
        cc.chou@...iatek.com, jiajie.hao@...iatek.com,
        alice.chao@...iatek.com
Subject: Re: [RFC PATCH v1] scsi: ufs: Remove pre-defined initial VCC voltage
 values

On Mon 30 Nov 03:16 CST 2020, Stanley Chu wrote:

> UFS specficication allows different VCC configurations for UFS devices,
> for example,
> 	(1). 2.70V - 3.60V (By default)
> 	(2). 1.70V - 1.95V (Activated if "vcc-supply-1p8" is declared in
>                           device tree)
> 	(3). 2.40V - 2.70V (Supported since UFS 3.x)
> 
> With the introduction of UFS 3.x products, an issue is happening that
> UFS driver will use wrong "min_uV/max_uV" configuration to toggle VCC
> regulator on UFU 3.x products with VCC configuration (3) used.
> 
> To solve this issue, we simply remove pre-defined initial VCC voltage
> values in UFS driver with below reasons,
> 
> 1. UFS specifications do not define how to detect the VCC configuration
>    supported by attached device.
> 
> 2. Device tree already supports standard regulator properties.
> 
> Therefore VCC voltage shall be defined correctly in device tree, and
> shall not be changed by UFS driver. What UFS driver needs to do is simply
> enabling or disabling the VCC regulator only.
> 
> This is a RFC conceptional patch. Please help review this and feel
> free to feedback any ideas. Once this concept is accepted, and then
> I would post a more completed patch series to fix this issue.
> 
> Signed-off-by: Stanley Chu <stanley.chu@...iatek.com>

Reviewed-by: Bjorn Andersson <bjorn.andersson@...aro.org>


This is the correct thing to do and I would prefer that we did the same
for vccq and vccq2 as well - and thereby remove the min_uV and max_uV
from ufs_vreg.

Regards,
Bjorn

> ---
>  drivers/scsi/ufs/ufshcd-pltfrm.c | 10 +---------
>  1 file changed, 1 insertion(+), 9 deletions(-)
> 
> diff --git a/drivers/scsi/ufs/ufshcd-pltfrm.c b/drivers/scsi/ufs/ufshcd-pltfrm.c
> index a6f76399b3ae..3965be03c136 100644
> --- a/drivers/scsi/ufs/ufshcd-pltfrm.c
> +++ b/drivers/scsi/ufs/ufshcd-pltfrm.c
> @@ -133,15 +133,7 @@ static int ufshcd_populate_vreg(struct device *dev, const char *name,
>  		vreg->max_uA = 0;
>  	}
>  
> -	if (!strcmp(name, "vcc")) {
> -		if (of_property_read_bool(np, "vcc-supply-1p8")) {
> -			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;
> -		}
> -	} else if (!strcmp(name, "vccq")) {
> +	if (!strcmp(name, "vccq")) {
>  		vreg->min_uV = UFS_VREG_VCCQ_MIN_UV;
>  		vreg->max_uV = UFS_VREG_VCCQ_MAX_UV;
>  	} else if (!strcmp(name, "vccq2")) {
> -- 
> 2.18.0
>