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

["Asutosh Das (asd)" <asutoshd@codeaurora.org>]

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@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?

Am open to other ideas though.

-asd

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