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

[nguyenb at quicinc.com]

On 2020-11-30 22:54, Stanley Chu wrote:
> 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
While we are on this topic, another similar concern is how to set the 
UFS's regulators loading to Low Power Mode (LPM).
Currently, the UFS_VREG_LPM_LOAD_UA is hardcoded to 1mA in the driver, 
and it is invoked by the ufshcd_config_vreg_lpm().
However, for some platforms, to put the regulators into LPM mode, it may 
be a different value than 1mA.
Should we be using ufs_vreg's min_uA in the ufshcd_config_vreg_lpm() 
instead of using the hardcoded value?
And the ufs_vreg's min_uA value would be parsed by the vendor's code?
We can post a proposal if this sounds ok.

Regards,
Bao

> 
> 
>> 
>> > 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
>> 
>>