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

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Date:   Mon, 30 Nov 2020 17:14:37 -0600
From:   Bjorn Andersson <bjorn.andersson@...aro.org>
To:     "Asutosh Das (asd)" <asutoshd@...eaurora.org>
Cc:     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, 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, 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 16:51 CST 2020, Asutosh Das (asd) wrote:

> 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.
> 

What is the actual voltage requirement for these devices and how does
the software know what voltage to pick in this range?

Regards,
Bjorn

> -asd
> 
> 
> -- 
> The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
> Linux Foundation Collaborative Project