Russell King - ARM Linux wrote:
On Mon, Dec 05, 2011 at 06:35:56PM +0100, Ulf Hansson wrote:
Instead of reading a register value everytime we need to
apply a new value for it, maintain a cached copy for it.
This also means we are able to skip writes that are not
needed.
I'm not sure this is a good idea. The ARM Primecells require a certain
number of bus clocks and MCLK periods between writes to both these
registers, and reading them back helps to ensure that we conform to
that requirement. Maintaining a cached copy of them allows faster
writes to these registers which could cause that requirement to be
violated.
You are definitely right. But how do we know that reading the register
value is enough?
What you could do is read the register, modify, and check whether the
modification has had any effect before writing it back. That will
allow unnecessary writes to still be skipped.
That could work. Do you want me to fixup the patch to include this "read
before write" mechanism then?
BR
Ulf Hansson
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