[PATCH 2/2] ARM: imx6q: replace clk_register_clkdev with clock DT lookup
Russell King - ARM Linux
linux at arm.linux.org.uk
Tue Aug 21 22:27:53 EST 2012
On Mon, Aug 20, 2012 at 12:22:56PM -0500, Matt Sealey wrote:
> You're going to have to define these clocks as a tree with parents and
> leaf nodes anyway in the clock subsystem. Why not define these in the
> device tree in total and reference them by handle when you build the
> entire clock tree from the ground up? Or will it just be all the
> clocks defined in Linux, but the lookups (which is what I see here)
> moved into the DT? Why not form the lookups as part of the definition
> of the clock tree?
Well, IMHO the DT conversion of the clk lookup stuff has been done
completely wrong.
What should have been done is rather than invent a totally new bloody
lookup interface that drivers have to use instead of clk_get(), is to
embed the OF lookup _inside_ clk_get().
What you do is this:
1. Have property names in the device node like:
clock_<connection-id> = <&provider-node output>
In the case of a NULL connection id:
clock = <&provider-node output>
Remember that the connection ID is _supposed_ to be something that
is described by the hardware (like - for the AACI primecell, the
clock which runs the functional side is called "AACICLK" by the TRM,
and for the MMCI primecell, it's "MMCICLK" - even though these two
clocks may be fed by the same source in an implementation.)
2. clkdev's lookup is then modified to look at the struct device, and
check for a DT node. If there is a DT node, it formats a property
string:
if (dev->of_node) {
char *propname, *clk_prop = NULL;
struct property *p;
if (conn_id) {
clk_prop = kasprintf("clock_%s", conn_id);
propname = clk_prop;
} else {
propname = "clock";
}
p = of_find_property(dev->of_node, propname, NULL);
if (clk_prop)
kfree(clk_prop);
if (p) {
clk = clk_get_from_of_property(p);
if (clk)
return clk;
}
/* Fallthrough to clkdev table lookup */
}
So now, you're not dealing with inventing a whole load of names for clocks
on a platform, instead what you're doing is describing _where_ the clock
comes from in the system for a particular device by device node and index
into it - just like we do for interrupts.
This means there's no need for huge tables and such like of clock names.
I did mention this idea long ago but got ignored.
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