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Commit 9d4164b5 authored by Nicholas Troast's avatar Nicholas Troast
Browse files

qcom-charger: fg-util: add float decode function 



Some SRAM registers are encoded using a floating point representation.
Add a function to decode these registers into signed micro-unit
integers.

The exponent and mantissa are signed integers represented by two's
complement, and the exponent value is offset by -9. This is a half
float representation stored as:

EEEEE MMMMMMMMMMM

Where E are the exponent bits, and M are the mantissa bits.

To decode this representation the following formula is applied:
2^(exponent - 9) * mantissa

Change-Id: Id9f28a0eeb2a904aca41eb46d0215d80287e0b88
Signed-off-by: default avatarNicholas Troast <ntroast@codeaurora.org>
parent 654b1238

drivers/power/qcom-charger/fg-core.h

+1 −0
Original line number Diff line number Diff line
@@ -252,4 +252,5 @@ extern int fg_ima_init(struct fg_chip *chip); 
extern int fg_sram_debugfs_create(struct fg_chip *chip);

extern void fill_string(char *str, size_t str_len, u8 *buf, int buf_len);

extern int64_t twos_compliment_extend(int64_t val, int s_bit_pos);

extern s64 fg_float_decode(u16 val);

#endif

drivers/power/qcom-charger/fg-util.c

+20 −0
Original line number Diff line number Diff line
@@ -29,6 +29,26 @@ static struct fg_dbgfs dbgfs_data = { 
	},

};



#define EXPONENT_SHIFT		11

#define EXPONENT_OFFSET		-9

#define MANTISSA_SIGN_BIT	10

#define MICRO_UNIT		1000000

s64 fg_float_decode(u16 val)

{

	s8 exponent;

	s32 mantissa;



	/* mantissa bits are shifted out during sign extension */

	exponent = ((s16)val >> EXPONENT_SHIFT) + EXPONENT_OFFSET;

	/* exponent bits are shifted out during sign extension */

	mantissa = sign_extend32(val, MANTISSA_SIGN_BIT) * MICRO_UNIT;



	if (exponent < 0)

		return (s64)mantissa >> -exponent;



	return (s64)mantissa << exponent;

}



void fill_string(char *str, size_t str_len, u8 *buf, int buf_len)

{

	int pos = 0;