On 20120503-19:13, Peter De Schrijver wrote: > Hi, > > I started looking into what would be needed to move our tegra30 clock code > to the common clock framework. The tegra30 clocktree is rather flat. Basically > there are a bunch of sources (13 PLLs, external audio clocks, osc and 32Khz) > and peripheral clocks which have a mux (with 4 or more inputs), a divider and > a gate. So almost every peripheral clock can have multiple parents. > > Some questions: > > 1) should these peripheral clocks be modelled as 3 different clocks > (mux -> divider -> gate) or would it be better to make a new clock type for > this? > That is really for you to decide. If the semantics of the existing mux, divider and gate in drivers/clk/clk-*.c work well for you then I think the answer is "yes". There is infrastructure for register-access locking in those common types which might help your complex clocks. Thanks to the parent rate propagation stuff in clk_set_rate it should be possible for your drivers to only be aware of the gate and call clk_set_rate on only that clock, which propagates up to the divider and, if necessary, again propagates up to the mux. I encourage you to try that first. But if you find the semantics of those basic clock types aren't cutting it for you then you must create a type which is platform-specific. > 2) how to define the default parent? in many cases the hw reset value isn't > a very sensible choice, so the kernel probably needs to set a parent of > many of them if we don't want to rely on bootloader configuration. The only related thing handled at the framework level is _discovery_ of the parent during clock registration/initialization. If you don't trust the bootloader and want to set things up as soon as possible (a wise move) then I suggest you do so from your platform clock code at the same time that you register your clocks with the framework. Something like: struct clk *c; c = clk_register(...); if (IS_ERR(c)) omg_fail(); clk_set_parent(c, b); Where 'b' is a parent of 'c'. Register your clock tree top-down and you can re-parent as you go. Regards, Mike -- To unsubscribe from this list: send the line "unsubscribe linux-tegra" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
