• Mark Brown's avatar
    regmap: Add maple tree based register cache · f033c26d
    Mark Brown authored
    The current state of the art for sparse register maps is the
    rbtree cache.  This works well for most applications but isn't
    always ideal for sparser register maps since the rbtree can get
    deep, requiring a lot of walking.  Fortunately the kernel has a
    data structure intended to address this very problem, the maple
    tree.  Provide an initial implementation of a register cache
    based on the maple tree to start taking advantage of it.
    
    The entries stored in the maple tree are arrays of register
    values, with the maple tree keys holding the register addresses.
    We store data in host native format rather than device native
    format as we do for rbtree, this will be a benefit for devices
    where we don't marshal data within regmap and simplifies the code
    but will result in additional CPU overhead when syncing the cache
    on devices where we do marshal data in regmap.
    
    This should work well for a lot of devices, though there's some
    additional areas that could be looked at such as caching the
    last accessed entry like we do for rbtree and trying to minimise
    the maple tree level locking. We should also use bulk writes
    rather than single register writes when resyncing the cache where
    possible, even if we don't store in device native format.
    
    Very small register maps may continue to to better with rbtree
    longer term.
    Signed-off-by: default avatarMark Brown <broonie@kernel.org>
    Link: https://lore.kernel.org/r/20230325-regcache-maple-v3-2-23e271f93dc7@kernel.orgSigned-off-by: default avatarMark Brown <broonie@kernel.org>
    f033c26d
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