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

[Stanley Chu]

Hi Asutosh,

On Mon, 2020-11-30 at 19:07 -0800, Asutosh Das (asd) wrote:
> On 11/30/2020 5:25 PM, Stanley Chu wrote:
> > 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.
> > 
> 
> I think this would work. Do you plan to implement this?
> If not, I can take this up. Please let me know.

Thanks for the understanding and support.

I would like to re-post this patch to simply removing the pre-defined
initial values of all device powers.

For vop idea supporting the voltage detection way, could you please take
it up since this would be better to fit what you need for fixing this
issue?

Thanks,
Stanley Chu


> 
> > 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
> >>
> > 
> 
> -asd
> 
>