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    SubjectRe: [PATCH v4 2/2] arm64: dts: sc7180: Add required-opps for i2c
    On Mon 19 Jul 04:37 CDT 2021, Rajendra Nayak wrote:

    >
    >
    > On 7/17/2021 3:29 AM, Bjorn Andersson wrote:
    > > On Fri 16 Jul 16:49 CDT 2021, Stephen Boyd wrote:
    > >
    > > > Quoting Bjorn Andersson (2021-07-16 13:52:12)
    > > > > On Fri 16 Jul 15:21 CDT 2021, Stephen Boyd wrote:
    > > > >
    > > > > > Quoting Bjorn Andersson (2021-07-16 13:18:56)
    > > > > > > On Fri 16 Jul 05:00 CDT 2021, Rajendra Nayak wrote:
    > > > > > >
    > > > > > > > qup-i2c devices on sc7180 are clocked with a fixed clock (19.2 MHz)
    > > > > > > > Though qup-i2c does not support DVFS, it still needs to vote for a
    > > > > > > > performance state on 'CX' to satisfy the 19.2 Mhz clock frequency
    > > > > > > > requirement.
    > > > > > > >
    > > > > > >
    > > > > > > Sounds good, but...
    > > > > > >
    > > > > > > > Use 'required-opps' to pass this information from
    > > > > > > > device tree, and also add the power-domains property to specify
    > > > > > > > the CX power-domain.
    > > > > > > >
    > > > > > >
    > > > > > > ..is the required-opps really needed with my rpmhpd patch in place?
    > > > > > >
    > > > > >
    > > > > > Yes? Because rpmhpd_opp_low_svs is not the lowest performance state for
    > > > > > CX.
    > > > >
    > > > > On e.g. sm8250 the first available non-zero corner presented in cmd-db
    > > > > is low_svs.
    >
    > what rail is this? the mmcx? Perhaps it does not support RET.
    > cx usually supports both collapse state and RET.
    >

    That was the one I was specifically looking at for the MDSS_GDSC->MMCX
    issue, so it's likely I didn't look elsewhere.

    > > >
    > > > Indeed. On sc7180 it's not the first non-zero corner. I suppose
    > > > retention for CX isn't actually used when the SoC is awake so your
    > > > rpmhpd patch is putting in a vote for something that doesn't do anything
    > > > at runtime for CX? I imagine that rpmh only sets the aggregate corner to
    > > > retention when the whole SoC is suspended/sleeping, otherwise things
    > > > wouldn't go very well. Similarly, min_svs may be VDD minimization? If
    > > > so, those first two states are basically states that shouldn't be used
    > > > at runtime, almost like sleep states.
    > > >
    > >
    > > But if that's the case, I don't think it's appropriate for the "enabled
    > > state" of the domain to use any of those corners.
    >
    > I rechecked the downstream kernels where all this voting happens from within
    > the clock drivers, and I do see votes to min_svs for some clocks, but Stephen is
    > right that RET is not something that's voted on while in active state.
    >
    > But always going with something just above the ret level while active will also
    > not work for all devices, for instance for i2c on 7180, it needs a cx vote of
    > low svs while the rail (cx) does support something lower than that which is min svs.
    > (why can't it just work with min svs?, I don't know, these values and recommendations
    > come in from the voltage plans published by HW teams for every SoC and we just end up
    > using them in SW, perhaps something to dig further and understand which I will try and
    > do but these are the values in voltage plans and downstream kernels which work for now)
    >

    So to some degree this invalidates my argumentation about the
    enabled_corner in rpmhpd, given that "enabled" means a different corner
    for each rail - not just the one with lowest non-zero value.

    So perhaps instead of introducing the enabled_corner we need to
    introduce your patch and slap a WARN_ON(corner == 0) in
    rpmhpd_power_on() - to ensure that all clients that uses a rpmhpd domain
    actually do vote for a high enough corner?

    Regards,
    Bjorn

    > >
    > > As this means that anyone who needs any of the rpmhpd domains active
    > > also needs to specify required-opps, which wouldn't be needed for any
    > > other power domain provider.
    > >
    > > And more importantly it means that a device sitting in a GDSC, which
    > > would be parented by a rpmhpd domain has no way to specify the GDSC and
    > > trickle the minimum-vote up to the rpmhpd domain. (And I know that we
    > > don't describe the parentship of the GDSCs today, but this patch
    > > tells me that it's around the corner - for more than MMCX)
    > >
    > > Regards,
    > > Bjorn
    > >
    > > > >
    > > > > And if this (which?) clock requires a higher corner than the lowest
    > > > > possible in order to tick at this "lowest" frequency, I'm certainly
    > > > > interested in some more details.
    > > > >
    >
    > --
    > QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a member
    > of Code Aurora Forum, hosted by The Linux Foundation

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