lrng_es_timer_common.h

/* SPDX-License-Identifier: GPL-2.0 OR BSD-2-Clause */
/*
 * LRNG Slow Noise Source: Time stamp array handling
 *
 * Copyright (C) 2022, Stephan Mueller <smueller@chronox.de>
 */

#ifndef _LRNG_ES_TIMER_COMMON_H
#define _LRNG_ES_TIMER_COMMON_H

bool lrng_gcd_tested(void);
void lrng_gcd_set(u32 running_gcd);
u32 lrng_gcd_get(void);
u32 lrng_gcd_analyze(u32 *history, size_t nelem);
void lrng_gcd_add_value(u32 time);
bool lrng_highres_timer(void);

/*
 * To limit the impact on the interrupt handling, the LRNG concatenates
 * entropic LSB parts of the time stamps in a per-CPU array and only
 * injects them into the entropy pool when the array is full.
 */

/* Store multiple integers in one u32 */
#define LRNG_DATA_SLOTSIZE_BITS		(8)
#define LRNG_DATA_SLOTSIZE_MASK		((1 << LRNG_DATA_SLOTSIZE_BITS) - 1)
#define LRNG_DATA_ARRAY_MEMBER_BITS	(4 << 3) /* ((sizeof(u32)) << 3) */
#define LRNG_DATA_SLOTS_PER_UINT	(LRNG_DATA_ARRAY_MEMBER_BITS / \
					 LRNG_DATA_SLOTSIZE_BITS)

/*
 * Number of time values to store in the array - in small environments
 * only one atomic_t variable per CPU is used.
 */
#define LRNG_DATA_NUM_VALUES		(CONFIG_LRNG_COLLECTION_SIZE)
/* Mask of LSB of time stamp to store */
#define LRNG_DATA_WORD_MASK		(LRNG_DATA_NUM_VALUES - 1)

#define LRNG_DATA_SLOTS_MASK		(LRNG_DATA_SLOTS_PER_UINT - 1)
#define LRNG_DATA_ARRAY_SIZE		(LRNG_DATA_NUM_VALUES /	\
					 LRNG_DATA_SLOTS_PER_UINT)

/* Starting bit index of slot */
static inline unsigned int lrng_data_slot2bitindex(unsigned int slot)
{
	return (LRNG_DATA_SLOTSIZE_BITS * slot);
}

/* Convert index into the array index */
static inline unsigned int lrng_data_idx2array(unsigned int idx)
{
	return idx / LRNG_DATA_SLOTS_PER_UINT;
}

/* Convert index into the slot of a given array index */
static inline unsigned int lrng_data_idx2slot(unsigned int idx)
{
	return idx & LRNG_DATA_SLOTS_MASK;
}

/* Convert value into slot value */
static inline unsigned int lrng_data_slot_val(unsigned int val,
					      unsigned int slot)
{
	return val << lrng_data_slot2bitindex(slot);
}

/*
 * Return the pointers for the previous and current units to inject a u32 into.
 * Also return the mask which the u32 word is to be processed.
 */
static inline void lrng_data_split_u32(u32 *ptr, u32 *pre_ptr, u32 *mask)
{
	/* ptr to previous unit */
	*pre_ptr = (*ptr - LRNG_DATA_SLOTS_PER_UINT) & LRNG_DATA_WORD_MASK;
	*ptr &= LRNG_DATA_WORD_MASK;

	/* mask to split data into the two parts for the two units */
	*mask = ((1 << (*pre_ptr & (LRNG_DATA_SLOTS_PER_UINT - 1)) *
			LRNG_DATA_SLOTSIZE_BITS)) - 1;
}

#endif /* _LRNG_ES_TIMER_COMMON_H */