// SPDX-License-Identifier: GPL-2.0
/* Copyright(c) 1999 - 2018 Intel Corporation. */
#include "ixgbe.h"
#include <linux/ptp_classify.h>
#include <linux/clocksource.h>
/*
* The 82599 and the X540 do not have true 64bit nanosecond scale
* counter registers. Instead, SYSTIME is defined by a fixed point
* system which allows the user to define the scale counter increment
* value at every level change of the oscillator driving the SYSTIME
* value. For both devices the TIMINCA:IV field defines this
* increment. On the X540 device, 31 bits are provided. However on the
* 82599 only provides 24 bits. The time unit is determined by the
* clock frequency of the oscillator in combination with the TIMINCA
* register. When these devices link at 10Gb the oscillator has a
* period of 6.4ns. In order to convert the scale counter into
* nanoseconds the cyclecounter and timecounter structures are
* used. The SYSTIME registers need to be converted to ns values by use
* of only a right shift (division by power of 2). The following math
* determines the largest incvalue that will fit into the available
* bits in the TIMINCA register.
*
* PeriodWidth: Number of bits to store the clock period
* MaxWidth: The maximum width value of the TIMINCA register
* Period: The clock period for the oscillator
* round(): discard the fractional portion of the calculation
*
* Period * [ 2 ^ ( MaxWidth - PeriodWidth ) ]
*
* For the X540, MaxWidth is 31 bits, and the base period is 6.4 ns
* For the 82599, MaxWidth is 24 bits, and the base period is 6.4 ns
*
* The period also changes based on the link speed:
* At 10Gb link or no link, the period remains the same.
* At 1Gb link, the period is multiplied by 10. (64ns)
* At 100Mb link, the period is multiplied by 100. (640ns)
*
* The calculated value allows us to right shift the SYSTIME register
* value in order to quickly convert it into a nanosecond clock,
* while allowing for the maximum possible adjustment value.
*
* These diagrams are only for the 10Gb link period
*
* SYSTIMEH SYSTIMEL
* +--------------+ +--------------+
* X540 | 32 | | 1 | 3 | 28 |
* *--------------+ +--------------+
* \________ 36 bits ______/ fract