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

[Asutosh Das (asd)]

On 11/30/2020 3:14 PM, Bjorn Andersson wrote:
> 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@xxxxxxxxxxxx>
> > > ---
> > >    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

For platforms that support both 2.x (2.7v-3.6v) and 3.x (2.4v-2.7v), the 
voltage requirements (Vcc) are 2.4v-3.6v. The software initializes the 
ufs device at 2.95v & reads the version and if the device is 3.x, it may 
do the following:
- Set the device power mode to SLEEP
- Disable the Vcc
- Enable the Vcc and set it to 2.5v
- Set the device power mode to ACTIVE

All of the above may be done at HS-G1 & moved to max supported gear 
based on the device version, perhaps?

Am open to other ideas though.

-asd

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