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

From: Rafael J. Wysocki
Date: Tue May 18 2021 - 05:36:58 EST

On Tue, May 18, 2021 at 5:42 AM Srinivas Pandruvada
<srinivas.pandruvada@xxxxxxxxxxxxxxx> 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@xxxxxxxxxxxxxxx>
> ---
> 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@xxxxxxxxxxxxxxx
> 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/fivr_switching_freq_mhz
> +Date: June, 2021
> +KernelVersion: v5.14
> +Contact: linux-acpi@xxxxxxxxxxxxxxx
> +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.

I can make this change when applying the patch.

> +
> +What: /sys/bus/platform/devices/INTC1045:00/pch_fivr_switch_frequency/fivr_switching_fault_status
> +Date: June, 2021
> +KernelVersion: v5.14
> +Contact: linux-acpi@xxxxxxxxxxxxxxx
> +Description:
> + (RO) Read the FIVR switching frequency control fault status.
> +
> +What: /sys/bus/platform/devices/INTC1045:00/pch_fivr_switch_frequency/ssc_clock_info
> +Date: June, 2021
> +KernelVersion: v5.14
> +Contact: linux-acpi@xxxxxxxxxxxxxxx
> +Description:
> + (RO) Presents SSC (spread spectrum clock) information for EMI
> + (Electro magnetic interference) control. This is a bit mask.
> + 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.
> diff --git a/drivers/acpi/dptf/dptf_pch_fivr.c b/drivers/acpi/dptf/dptf_pch_fivr.c
> index 5fca18296bf6..22c4ae0401ef 100644
> --- a/drivers/acpi/dptf/dptf_pch_fivr.c
> +++ b/drivers/acpi/dptf/dptf_pch_fivr.c
> @@ -55,15 +55,24 @@ static ssize_t name##_store(struct device *dev,\
>
> PCH_FIVR_SHOW(freq_mhz_low_clock, GFC0)
> PCH_FIVR_SHOW(freq_mhz_high_clock, GFC1)
> +PCH_FIVR_SHOW(ssc_clock_info, GEMI)
> +PCH_FIVR_SHOW(fivr_switching_freq_mhz, GFCS)
> +PCH_FIVR_SHOW(fivr_switching_fault_status, GFFS)
> PCH_FIVR_STORE(freq_mhz_low_clock, RFC0)
> PCH_FIVR_STORE(freq_mhz_high_clock, RFC1)
>
> static DEVICE_ATTR_RW(freq_mhz_low_clock);
> static DEVICE_ATTR_RW(freq_mhz_high_clock);
> +static DEVICE_ATTR_RO(ssc_clock_info);
> +static DEVICE_ATTR_RO(fivr_switching_freq_mhz);
> +static DEVICE_ATTR_RO(fivr_switching_fault_status);
>
> static struct attribute *fivr_attrs[] = {
> &dev_attr_freq_mhz_low_clock.attr,
> &dev_attr_freq_mhz_high_clock.attr,
> + &dev_attr_ssc_clock_info.attr,
> + &dev_attr_fivr_switching_freq_mhz.attr,
> + &dev_attr_fivr_switching_fault_status.attr,
> NULL
> };
>
> --
> 2.27.0
>