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

[Stanley Chu]

On Mon, 2020-11-30 at 15:54 -0800, Asutosh Das (asd) wrote:
> 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 at mediatek.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
> 
> 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?

Hi Asutosh,

Thanks for sharing this idea.

1. I did not see above flow defined in UFS specifications, please
correct me if I was wrong.

2. For above flow, the concern is that I am not sure if all devices
supporting VCC (2.4v - 2.7v) can accept higher voltage, say 2.95v, for
version detection.

3. For version detection, another concern is that I am not sure if all
3.x devices support VCC (2.4v - 2.7v) only, or in other words, I am not
sure if all 2.x devices support VCC (2.7v - 3.6v) only. The above rule
will break any devices not obeying this "conventions".

For platforms that support both 2.x (2.7v-3.6v) and 3.x (2.4v-2.7v),

It would be good for UFS drivers detecting the correct voltage if the
protocol is well-defined in specifications. Until that day, any
"non-standard" way may be better implemented in vendor's ops?

If the vop concept works on your platform, we could still keep struct
ufs_vreg and allow vendors to configure proper min_uV and max_uV to make
regulator_set_voltage() works during VCC toggling flow. Without specific
vendor configurations, min_uV and max_uV would be NULL by default and
UFS core driver will only enable/disasble VCC regulator only without
adjusting its voltage.

Maybe one possible another idea is to decide the correct voltage and
configure regulator properly before kernel?

Thanks,
Stanley Chu

> 
> Am open to other ideas though.
> 
> -asd
>