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SubjectRe: [RFC PATCH v1] scsi: ufs: Remove pre-defined initial VCC voltage values
On 2020-12-01 11:19, Asutosh Das (asd) wrote:
> On 11/30/2020 6:53 PM, Bjorn Andersson wrote:
>> On Mon 30 Nov 17:54 CST 2020, 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@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.
>>>
>>
>> But that means that for a board where we don't know (don't want to
>> know)
>> if we have a 2.x or 3.x device we need to set:
>>
>> regulator-min-microvolt = <2.4V>
>> regulator-max-microvolt = <3.6V>
>>
>> And the 2.5V and the two ranges should be hard coded into the ufshcd
>> (in
>> particular if they come from the specification).
>>
>> For devices with only 2.x or 3.x devices,
>> regulator-{min,max}-microvolt
>> should be adjusted accordingly.
>>
>> Note that driving the regulators outside these ranges will either
>> damage
>> the hardware or cause it to misbehave, so these values should be
>> defined
>> in the board.dts anyways.
>>
>> Also note that regulator_set_voltage(2.4V, 3.6V) won't give you "a
>> voltage between 2.4V and 3.6V, it will most likely give either 2.4V or
>> any more specific voltage that we've specified in the board file
>> because
>> the regulator happens to be shared with some other consumer and
>> changing
>> it in runtime would be bad.
>>
>> Regards,
>> Bjorn
>>
>
> Understood.
> I also understand that assumptions on the regulator limits in the
> driver is a bad idea. I'm not sure how it's designed, but I should
> think the power-grid design should take care of regulator sharing; if
> it's being shared and the platform supports both 2.x and 3.x. Perhaps,
> such platforms be identified using a dts flag - not sure if that's
> such a good idea though.
>
> I like Stanley's proposal of a vops and let vendors handle it, until
> specs or someone has a better suggestion.

Agree, vops is all we need as of now, please upload a change to add one
properly.

Thanks,

Can Guo.

>
> -asd

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