Re: [PATCH V2 4/6] regulator: qcom_smd: Add support to define the bootup voltage

[Devi Priya]

On 3/6/2023 6:39 PM, Devi Priya wrote:
> On 3/3/2023 6:57 PM, Konrad Dybcio wrote:
> > On 3.03.2023 14:21, Devi Priya wrote:
> > > On 2/23/2023 4:31 AM, Mark Brown wrote:
> > > > On Wed, Feb 22, 2023 at 11:11:42PM +0100, Konrad Dybcio wrote:
> > > >
> > > > > Thinking about it again, this seems like something that could be
> > > > > generalized and introduced into regulator core.. Hardcoding this
> > > > > will not end well.. Not to mention it'll affect all mp5496-using
> > > > > boards that are already upstream.
> > > >
> > > > > WDYT about regulator-init-microvolts Mark?
> > > >
> > > > The overwhelming majority of devices that have variable voltages
> > > > support readback, these Qualcomm firmware devices are pretty much
> > > > unique in this regard.  We don't want a general property to set a
> > > > specific voltage since normally we should be using the
> > > > constraints and don't normally need to adjust things immediately
> > > > since we can tell what the current voltage is.
> > > >
> > > > This is pretty much just going to be a device specific bodge,
> > > > ideally something that does know what the voltage is would be
> > > > able to tell us at runtime but if that's not possible then
> > > > there's no good options.  If the initial voltage might vary based
> > > > on board then a device specific DT property might be less
> > > > terrible, if it's determined by the regulator the current code
> > > > seems fine.  Or just leave the current behavour, if the
> > > > constraints are accurate then hopefully a temporary dip in
> > > > voltage is just inelegant rather than an issue.  Indeed the
> > > > current behaviour might well save power if you've got a voltage
> > > > range configured and nothing actually ever gets round to setting
> > > > the voltage (which is depressingly common, people seem keen on
> > > > setting voltage ranges even when the voltage is never varied in
> > > > practice).
> > >
> > > Hi Mark, The initial bootup voltage is actually blown into the OTP 
> > > register of the PMIC and it remains the same across boards for 
> > > IPQ9574 SoC.
> > But what about IPQ6018 which also uses MP5496? That's also gonna
> > set the voltage on there, it may be too high/low..
For IPQ6018, the bootup voltage is the same as that of IPQ9574 which is
875mV
> >   Initially the SoC runs at 800MHz with a voltage of 875mV set by the 
> > bootloaders. As kernel does not know the initial voltage, during 
> > regulator registration the framework considers the current voltage to 
> > be zero and tries to bring up the regulator to minimum supported 
> > voltage of 600mV. This causes the dip which might be of concern in SS 
> > parts where the voltage might be insufficient leading to silent reboots.
> > That's an SoC-specific thing, the same regulator can be used with
> > many different ones. We can't just assume it'll always be like this.
> > I see the problem, but I believe this is not the correct solution
Okay, As we had discussions on reading back the voltage & the generic
DT property, do you suggest any other possible solutions here?
> > Konrad
> > > Best Regards,
> > > Devi Priya