On Wed, Mar 14, 2012 at 2:28 PM, Thomas Gleixner tglx@linutronix.de 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...
On Wed, Mar 14, 2012 at 1:48 AM, Sascha Hauer s.hauer@pengutronix.de wrote:
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