linux-kernel - Re: [PATCH v2] ACPI: DPTF: Add new PCH FIVR methods

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Date:   Fri, 21 May 2021 19:12:36 +0200
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>
Cc:     "Rafael J. Wysocki" <rafael@...nel.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Len Brown <lenb@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        ACPI Devel Maling List <linux-acpi@...r.kernel.org>
Subject: Re: [PATCH v2] ACPI: DPTF: Add new PCH FIVR methods

On Tue, May 18, 2021 at 12:27 PM Srinivas Pandruvada
<srinivas.pandruvada@...ux.intel.com> wrote:
>
> On Tue, 2021-05-18 at 11:36 +0200, Rafael J. Wysocki wrote:
> > On Tue, May 18, 2021 at 5:42 AM Srinivas Pandruvada
> > <srinivas.pandruvada@...ux.intel.com> wrote:
> > >
> > > Some additional information is required for updating PCH FIVR
> > > values
> > > upon WiFi channel changes.
> > >
> > > New attributes added to the existing sysfs:
> > > fivr_switching_freq_mhz : Get the FIVR switching control frequency
> > >                           using ACPI method GFCS. Refer to the
> > >                           documentation for the equation.
> > > fivr_switching_fault_status: Read the FIVR switching frequency
> > > control
> > >                         fault status. Uses ACPI method GFFS
> > >
> > > ssc_clock_info : Presents SSC (spread spectrum clock) information
> > > for EMI
> > > (Electro magnetic interference) control. Use ACPI method GEMI.
> > > Refer
> > > to the description of GEMI method below.
> > >
> > > GFFS
> > > This ACPI method is used to read the FIVR switching frequency
> > > control
> > > fault status.
> > > Bits    Description
> > > [0:0]   Fault status when set to 1
> > > [31:1]  Reserved
> > >
> > > GFCS
> > > This ACPI method is used to read the FIVR switching control
> > > frequency.
> > > Bits    Description
> > > [11:0]  Actual Frequency = value * XTAL_FREQ / 128
> > > [31:12] Reserved
> > >
> > > GEMI
> > > This ACPI method is used to read the programmed register value for
> > > EMI
> > > (Electro magnetic interference) control.
> > >
> > > Bits    Description
> > > [7:0]   Sets clock spectrum spread percentage:
> > >         0x00=0.2% , 0x3F=10%
> > >         1 LSB = 0.1% increase in spread (for
> > >         settings 0x01 thru 0x1C)
> > >         1 LSB = 0.2% increase in spread (for
> > >         settings 0x1E thru 0x3F)
> > > [8]     When set to 1, enables spread
> > >         spectrum clock
> > > [9]     0: Triangle mode. FFC frequency
> > >         walks around the Fcenter in a linear
> > >         fashion
> > >         1: Random walk mode. FFC frequency
> > >         changes randomly within the SSC
> > >         (Spread spectrum clock) range
> > > [10]    0: No white noise. 1: Add white noise
> > >         to spread waveform
> > > [11]    When 1, future writes are ignored.
> > >
> > > Signed-off-by: Srinivas Pandruvada <
> > > srinivas.pandruvada@...ux.intel.com>
> > > ---
> > > v2
> > >         Update documentation for fivr_switching_freq_mhz
> > >
> > >  Documentation/ABI/testing/sysfs-platform-dptf | 42
> > > +++++++++++++++++++
> > >  drivers/acpi/dptf/dptf_pch_fivr.c             |  9 ++++
> > >  2 files changed, 51 insertions(+)
> > >
> > > diff --git a/Documentation/ABI/testing/sysfs-platform-dptf
> > > b/Documentation/ABI/testing/sysfs-platform-dptf
> > > index 141834342a4d..fe62f024eb93 100644
> > > --- a/Documentation/ABI/testing/sysfs-platform-dptf
> > > +++ b/Documentation/ABI/testing/sysfs-platform-dptf
> > > @@ -111,3 +111,45 @@ Contact:   linux-acpi@...r.kernel.org
> > >  Description:
> > >                 (RW) The PCH FIVR (Fully Integrated Voltage
> > > Regulator) switching frequency in MHz,
> > >                 when FIVR clock is 38.4MHz.
> > > +
> > > +What:
> > > /sys/bus/platform/devices/INTC1045:00/pch_fivr_switch_frequency/fiv
> > > r_switching_freq_mhz
> > > +Date:          June, 2021
> > > +KernelVersion: v5.14
> > > +Contact:       linux-acpi@...r.kernel.org
> > > +Description:
> > > +               (RO) Get the FIVR switching control frequency in
> > > MHz after applying equation
> > > +               "fivr_switching_freq_mhz * XTAL_FREQ / 128". Here
> > > XTAL_FREQ is Crystal Oscillator frequency
> > > +               in MHz, which is product specific.
> >
> > IMO it would be sufficient to say the following here:
> >
> > +               (RO) PCH FIVR switching control frequency in the
> > units
> > of XTAL_FREQ / 128,
> > +               where XTAL_FREQ is the Crystal Oscillator frequency
> > (product specific).
> >
> > This means that it needs to be multiplied by XTAL_FREQ / 128 to get
> > the frequency in the whatever units XTAL_FREQ is expressed.
> >
> Looks good.

So applied as 5.14 material, thanks!