On Monday, August 24, 2015 at 02:49:24 PM, Russell King - ARM Linux wrote:

Hi Russell,

On Mon, Aug 24, 2015 at 01:03:51PM +0200, Marek Vasut wrote:

quoted

These are functions, not macros :)

btw is there any reason for these ? I'd say, just put the read*() and
write*() functions directly into the code and be done with it, it is
much less confusing.

Also, why do you use the _relaxed() versions of the functions ?

Now that the _relaxed() accessors are available throughout the kernel,
everyone should be using the _relaxed() versions unless they need the
properties of the non-relaxed versions.

You mean the memory barrier, right ?

Remember that the non-relaxed
versions are rather expensive on ARM due to the need to go all the way
out to the L2 cache - it at least doubles the number of accesses for
every read*/write*().

I think in case of this driver, we don't need the non-relaxed version
anywhere, right ? Thanks for the educational writeup :)

btw. is [1] still the current study material on the I/O accessor best
practices please ?

[1] http://permalink.gmane.org/gmane.linux.ports.arm.kernel/117644

Best regards,
Marek Vasut