linux-kernel - Re: [PATCH V1 0/3] scsi: ufs: Add a vops to configure VCC voltage level

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Date:   Mon, 08 Feb 2021 16:00:47 +0530
From:   nitirawa@...eaurora.org
To:     Avri Altman <Avri.Altman@....com>
Cc:     asutoshd@...eaurora.org, cang@...eaurora.org,
        stummala@...eaurora.org, vbadigan@...eaurora.org,
        alim.akhtar@...sung.com, jejb@...ux.ibm.com,
        martin.petersen@...cle.com, stanley.chu@...iatek.com,
        beanhuo@...ron.com, bvanassche@....org, linux-scsi@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH V1 0/3] scsi: ufs: Add a vops to configure VCC voltage
 level

On 2021-02-01 14:01, nitirawa@...eaurora.org wrote:
> On 2021-01-31 19:32, Avri Altman wrote:
>>> 
>>> UFS specification allows different VCC configurations for UFS 
>>> devices,
>>> for example,
>>>         (1)2.70V - 3.60V (For UFS 2.x devices)
>>>         (2)2.40V - 2.70V (For UFS 3.x devices)
>>> For platforms supporting both ufs 2.x (2.7v-3.6v) and
>>> ufs 3.x (2.4v-2.7v), the voltage requirements (VCC) is 2.4v-3.6v.
>>> So to support this, we need to start the ufs device initialization 
>>> with
>>> the common VCC voltage(2.7v) and after reading the device descriptor 
>>> we
>>> need to switch to the correct range(vcc min and vcc max) of VCC 
>>> voltage
>>> as per UFS device type since 2.7v is the marginal voltage as per 
>>> specs
>>> for both type of devices.
>>> 
>>> Once VCC regulator supply has been intialised to 2.7v and UFS device
>>> type is read from device descriptor, we follows below steps to
>>> change the VCC voltage values.
>>> 
>>> 1. Set the device to SLEEP state.
>>> 2. Disable the Vcc Regulator.
>>> 3. Set the vcc voltage according to the device type and reenable
>>>    the regulator.
>>> 4. Set the device mode back to ACTIVE.
>>> 
>>> The above changes are done in vendor specific file by
>>> adding a vops which will be needed for platform
>>> supporting both ufs 2.x and ufs 3.x devices.
>> The flow should be generic - isn't it?
>> Why do you need the entire flow to be vendor-specific?
>> Why not just the parameters vendor-specific?
>> 
>> Thanks,
>> Avri
> 
> Hi Avri,
> This vops change was done as per the below mail thread
> discussion where it was decided to go with vops and
> let vendors handle it, until specs provides more clarity.
> 
> https://www.spinics.net/lists/kernel/msg3754995.html
> 
> Regards,
> Nitin

Hi Avri,
Please let me know if you have any further comments on this.

Regards,
Nitin