Linux Device Drivers Development

regmap_update_bits function

regmap_update_bits is a three-in-one function. Its prototype is as follows:

int regmap_update_bits(struct regmap *map, unsigned int reg, 
         unsigned int mask, unsigned int val) 

It performs a read/modify/write cycle on the register map. It is a wrapper of _regmap_update_bits, which looks as follows:

static int _regmap_update_bits(struct regmap *map, 
                    unsigned int reg, unsigned int mask,  
                    unsigned int val, bool *change) 
{ 
    int ret; 
    unsigned int tmp, orig; 
 
    ret = _regmap_read(map, reg, &orig); 
    if (ret != 0) 
        return ret; 
 
    tmp = orig& ~mask; 
    tmp |= val & mask; 
 
    if (tmp != orig) { 
        ret = _regmap_write(map, reg, tmp); 
        *change = true; 
    } else { 
        *change = false; 
    } 
 
    return ret; 
} 

This way, bits you need to update must be set to