Messages in this thread | | | Date | Wed, 19 Dec 2012 10:03:26 +0100 | From | Sascha Hauer <> | Subject | Re: common clock framwork: clk_set_rate issue |
| |
On Wed, Dec 19, 2012 at 02:49:25PM +0800, Chao Xie wrote: > On Tue, Dec 18, 2012 at 3:47 PM, Sascha Hauer <s.hauer@pengutronix.de> wrote: > >> There is already a flag to do it. > >> CLK_SET_RATE_PARENT > > > > That flag has another meaning. It means that a clock is allowed to > > change the parents rate when a rate change is requested. What I meant > > is a flag that allows a mux to change its parent when a rate change is > > requested. > > > another flag can help it. what i mean is that i can clear the flag > CLK_SET_RATE_PARENT of MUX's children, so when clock changing will not > impact the MUX. > > >> if the mux does not want to changes the input for clk_set_rate called > >> by its child, it can clear this flag. > >> The question is whether we need add the round_rate/recalc_rate for MUX > >> type of clock? Is there any special issue about it that why current > >> MUX implementation does not have these callbacks? > > > > They currently do not need these callbacks. When a clock does not have > > round_rate propagates up to the parent if CLK_SET_RATE_PARENT is set or > > it returns the parents rate if this flag is not set. The situation with > > set_rate is similar. > > > So it means that for a uart clock that get its clock from > MUX --> DIV --> UART > when uart want to change its rate, the driver has to know the topology > of clock tree. It can not directly clk_set_rate(uart), because it only > change the DIV settings, and if we want to change the MUX input, we > have to invoke clk_set_parent(MUX). So the uart driver need to know > the clock tree topology, and it is not good for sharing a driver > between mutiple SOCs that has same UART controller IP. > That is what i am confused about.
A driver shouldn't need to know the clock topology. If you have a setup like described above and want to have the mux look for the best parent during rate change, then a new flag for the mux is needed, something like:
CLK_SET_RATE_SWITCH_PARENT (1 << x) /* allow to change parent on clk_set_rate /*
For the reasons I described earlier in this thread this would have to be optional as on i.MX I don't want magic parent changes to happen on a rate change.
Sascha
-- Pengutronix e.K. | | Industrial Linux Solutions | http://www.pengutronix.de/ | Peiner Str. 6-8, 31137 Hildesheim, Germany | Phone: +49-5121-206917-0 | Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-5555 |
| |