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Subject: Re: [RFC PATCH v1] scsi: ufs: Remove pre-defined initial VCC voltage
 values
To:     Stanley Chu <stanley.chu@mediatek.com>
Cc:     Bjorn Andersson <bjorn.andersson@linaro.org>,
        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>
 <1606785904.23925.25.camel@mtkswgap22>
From:   "Asutosh Das (asd)" <asutoshd@codeaurora.org>
Message-ID: <d998857a-1744-a8bb-1a3e-77166c171f37@codeaurora.org>
Date:   Mon, 30 Nov 2020 19:07:53 -0800
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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@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.

> 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


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