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Subject: Re: [RFC PATCH v1] scsi: ufs: Remove pre-defined initial VCC voltage
 values
To:     Bjorn Andersson <bjorn.andersson@linaro.org>
Cc:     Stanley Chu <stanley.chu@mediatek.com>, linux-scsi@vger.kernel.org,
        martin.petersen@oracle.com, avri.altman@wdc.com,
        alim.akhtar@samsung.com, jejb@linux.ibm.com, beanhuo@micron.com,
        cang@codeaurora.org, matthias.bgg@gmail.com, bvanassche@acm.org,
        linux-mediatek@lists.infradead.org,
        linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org,
        nguyenb@codeaurora.org, kuohong.wang@mediatek.com,
        peter.wang@mediatek.com, chun-hung.wu@mediatek.com,
        andy.teng@mediatek.com, chaotian.jing@mediatek.com,
        cc.chou@mediatek.com, jiajie.hao@mediatek.com,
        alice.chao@mediatek.com
References: <20201130091610.2752-1-stanley.chu@mediatek.com>
 <568660cd-80e6-1b8f-d426-4614c9159ff4@codeaurora.org>
 <X8V83T+Tx6teNLOR@builder.lan>
 <4335d590-0506-d920-8e7f-f0f0372780f9@codeaurora.org>
 <X8WwPs1MPg64FEp8@builder.lan>
From:   "Asutosh Das (asd)" <asutoshd@codeaurora.org>
Message-ID: <bf6e03ee-95ab-4768-7ce5-7f196ab6db60@codeaurora.org>
Date:   Mon, 30 Nov 2020 19:19:21 -0800
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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.

-asd


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