RE: [PATCH v2] scsi: ufs: Remove pre-defined initial voltage values of device powers

[Avri Altman]

> 
> UFS specficication allows different VCC configurations for UFS devices,
> for example,
>         (1). 2.70V - 3.60V (Activated by default in UFS core driver)
>         (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" values to configure the
> voltage of VCC regulator on UFU 3.x products with the configuration (3)
> used.
> 
> To solve this issue, we simply remove pre-defined initial VCC voltage
> values in UFS core 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 changed by UFS driver. What UFS driver needs to do is simply
> enable or disable the VCC regulator only.
> 
> Similar change is applied to VCCQ and VCCQ2 as well.
> 
> Note that we keep struct ufs_vreg unchanged. This is allow vendors to
> configure proper min_uV and max_uV of any regulators to make
> regulator_set_voltage() works during regulator toggling flow.
> Without specific vendor configurations, min_uV and max_uV will be NULL
> by default and UFS core driver will enable or disable the regulator
> only without adjusting its voltage.
> 
> Reviewed-by: Bjorn Andersson <bjorn.andersson@xxxxxxxxxx>
> Signed-off-by: Stanley Chu <stanley.chu@xxxxxxxxxxxx>
Acked-by: Avri Altman <avri.altman@xxxxxxx>