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 syncing the cache where possible, even if we don't store in device native format, and there is room for improvement in how we load register defaults into the cache. Very small register maps may continue to to better with rbtree longer term, though the difference should become marginal especially in the context of the cost of register I/O. Changes in v2: - Rework to store multiple values per maple tree node with coalescing, bringing us much closer to the state of the art with rbtree. - Add locking required for maple tree usage. - Use more efficent code suggested by Liam to free the register map. - Link to v1: https://lore.kernel.org/r/20230325-regcache-maple-v1-0-1c76916359fb@xxxxxxxxxx Signed-off-by: Mark Brown <broonie@xxxxxxxxxx> --- Mark Brown (2): regmap: Factor out single value register syncing regmap: Add maple tree based register cache drivers/base/regmap/Makefile | 2 +- drivers/base/regmap/internal.h | 2 + drivers/base/regmap/regcache-maple.c | 265 +++++++++++++++++++++++++++++++++++ drivers/base/regmap/regcache.c | 41 ++++-- drivers/base/regmap/regmap-kunit.c | 3 + include/linux/regmap.h | 1 + 6 files changed, 299 insertions(+), 15 deletions(-) --- base-commit: c20bc1c03695287bd19922a32052f2bc7d4a462d change-id: 20230325-regcache-maple-364e7581cf0c Best regards, -- Mark Brown <broonie@xxxxxxxxxx>
