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

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Date:   Mon, 30 Nov 2020 14:51:41 -0800
From:   "Asutosh Das (asd)" <asutoshd@...eaurora.org>
To:     Stanley Chu <stanley.chu@...iatek.com>, linux-scsi@...r.kernel.org,
        martin.petersen@...cle.com, avri.altman@....com,
        alim.akhtar@...sung.com, jejb@...ux.ibm.com
Cc:     beanhuo@...ron.com, 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, bjorn.andersson@...aro.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 11/30/2020 1:16 AM, 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>
> ---
>   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")) {
> 

Hi Stanley

Thanks for the patch. Bao (nguyenb) was also working towards something 
similar.
Would it be possible for you to take into account the scenario in which 
the same platform supports both 2.x and 3.x UFS devices?

These've different voltage requirements, 2.4v-3.6v.
I'm not sure if standard dts regulator properties can support this.

-asd


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