On Tue, Jun 18, 2013 at 04:11:16PM +0100, Russell King - ARM Linux wrote:

On Tue, Jun 18, 2013 at 05:02:49PM +0200, Linus Walleij wrote:

quoted

Nowadays I would do the above with regmap_update_bits().

quoted

Mutual exclusion for read-modify-write of individual bits in a
register is one of those cases where doing a regmap over
a memory-mapped register range makes a lot of sense.
(drivers/mfd/syscon.c being a nice example)

So, for that solution we need to have some kind of global regmap per
register or somesuch.  Then you run into regmap needing a struct
device - well, with a shared register, which struct device do you
use, or do you have to invent one?

That sounds more heavy-weight than is really necessary.

Yes, regmap is far too heavyweight for a lot of these things - it
shouldn't really go in performance critical at the CPU level paths, it's
designed around things where I/O costs are considerable and worth
avoiding.

I do think that this is a very good idea - with the I2C/SPI drivers I
was reviewing prior to regmap there were always just far too many simple
bugs with read/modify/write cycles so factoring out the code really
helped with review.
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