regmap rbtree cache

#define XXX_REG_STATUS  0x06
#define XXX_REG_CTRL0   0x07
#define XXX_REG_CTRL1   0x08

static bool xxx_is_writeable_reg(struct device *dev, unsigned int reg)
{
    switch (reg) {
    case XXX_REG_CTRL0:
    case XXX_REG_CTRL1:
        return true;
    default:
        return false;
    }
}

static bool xxx_is_readable_reg(struct device *dev, unsigned int reg)
{
    switch (reg) {
    case XXX_REG_XOUT_L:
    case XXX_REG_XOUT_H:
    case XXX_REG_YOUT_L:
    case XXX_REG_YOUT_H:
    case XXX_REG_ZOUT_L:
    case XXX_REG_ZOUT_H:
    case XXX_REG_STATUS:
    case XXX_REG_ID:
        return true;
    default:
        return false;
    }
}

static bool xxx_is_volatile_reg(struct device *dev, unsigned int reg)
{
    switch (reg) {
    case XXX_REG_CTRL0:
    case XXX_REG_CTRL1:
    case XXX_REG_STATUS:
        return false;
    default:
        return true;
    }
}

static struct reg_default xxx_reg_defaults[] = {
    { XXX_REG_CTRL0,  0x00 },
    { XXX_REG_CTRL1,  0x00 },
    { XXX_REG_STATUS, 0x00 },
};

static const struct regmap_config xxx_regmap_config = {
    .name = XXX_REGMAP_NAME,

    .reg_bits = 8,
    .val_bits = 8,

    .max_register = XXX_REG_ID,
    .cache_type = REGCACHE_RBTREE,

    .writeable_reg = xxx_is_writeable_reg,
    .readable_reg = xxx_is_readable_reg,
    .volatile_reg = xxx_is_volatile_reg,

    .reg_defaults = xxx_reg_defaults,
    .num_reg_defaults = ARRAY_SIZE(xxx_reg_defaults),
};