On Wed, Mar 14, 2012 at 2:28 PM, Thomas Gleixner [off-list ref] wrote:

On Wed, 14 Mar 2012, Turquette, Mike wrote:

Could you folks please trim your replies? It's annoying to page down a
gazillion of lines to find the gist.

Sure.  My mailer does this for me so I forget to do it sometimes...

quoted

On Wed, Mar 14, 2012 at 1:48 AM, Sascha Hauer [off-list ref] wrote:

quoted

quoted

Also, do you forsee needing hole in parent_names for any reason other
than described above?

I need it only for the case where a some values in the mux are marked as
reserved in the datasheet or we simply do not have the corresponding
clock in our tree (yet). We could also say that NULL pointers are not
allowed in parent arrays, but instead "orphan" or "dummy" should be
used. Then __clk_init should check for NULL pointers to make this clear.

I've added a WARN in __clk_init if any entries in .parent_names are
NULL. ?I think it best to populate it with "dummy", or maybe a
platform-specific name if it helps you during development.

There is no guarantee that the selection of a parent can be mapped
linear to register values.

Agreed.  I have always viewed .parent_names as only a list of the
names of all possible parents, nothing more.  And of course its array
indexing should line up with struct clk **parents.

So the right way to deal with it is to have an array of valid names
with no holes and NULL pointers allowed and have a mapping from the
array index to the register value.

This is essentially what the .set_rate callback does.  It takes as
input "u8 index" and peforms the hardware specific magic to select the
correct parent clock.  This might be a register write using that exact
same index, or it might be a single-bit register write using that
index as the shift value, or it might translate that index into the
data sent to an i2c device (where the address would be stored in
struct clk_foo), etc etc.

We both agree that .parent_names must contain valid names and should
not have holes.  What I don't understand is if you are saying that we
should allow NULL ptrs as names; that seems contradictory but I want
to make sure I'm reading you correctly.

Thanks,
Mike

That makes the core code robust and allows to handle all corner cases
including reserved bits, not implemented clocks and weird register
layouts.

Thanks,

? ? ? ?tglx