Messages in this thread | | | Date | Tue, 7 Jul 2015 18:46:06 -0700 | From | Stephen Boyd <> | Subject | Re: [PATCH v4 3/8] clk: add support for clocks provided by SCP(System Control Processor) |
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On 07/07, Sudeep Holla wrote: > > > On 06/07/15 20:52, Stephen Boyd wrote: > >> > > > >If I have time I may try to start doing the clk_register() conversion, > >but it will take a while so I doubt it will be in v4.3. I'm asking if > >you can add a clk_hw based API that does something like > >clk_set_rate_range() without requiring a struct clk pointer. i.e. > >clk_hw_set_rate_range(struct clk_hw *hw, min, max) that constraints the > >min/max rate of the clock. This way, the driver is only using clk > >provider APIs and not clk consumer APIs. > > > > I understand the intention of separating clk provider helpers/APIs > and clk consumer APIs. Since {min,max}_rate are part of struct clk > itself, I was thinking that you would have moved it to struct clk_core > as part of the rework you mentioned and hence asked about the patches. > > IIUC, if {min,max}_rate remain part of struct clk, then how are we > restricting that operation to just the clk providers ? clk consumer > can still directly modify or use clk_set_rate_range. > > Do we continue to provide that feature for both provider and consumer ? > If so I assume {min,max}_rate range requested by consumer should be > within the limits set by provider and do we maintain both the limits ? > > Sorry if I am missing something fundamental since I don't have much > knowledge of clk layer internals. >
Yes struct clk would have min/max, and struct clk_core would have min/max. Then some sort of provider API (or possibly even clk_init_data) would take the min/max fields and copy them over to struct clk_core. Then during set_rate operations we would aggregate the constraints from struct clk like we already do and add in the constrains in struct clk_core.
One downside to adding new fields to clk_init_data is that there are drivers out there that aren't initializing that structure to 0, and they're putting it on the stack, so stack junk can come through. Furthermore, min/max would mean that every driver needs to specify some large number for max or we have to special case min == max == 0 and ignore it. Somehow it needs to be opt-in. If we want to go down the clk_init_data route then perhaps we need some sort of rate_constraint struct pointer in there that drivers can optionally setup.
struct clk_rate_constraint { unsigned long min; unsigned long max; };
struct clk_init_data { ... struct clk_rate_constraint *rate_constraint; };
I haven't thought it through completely, but I can probably write up some patch tomorrow after I sleep on it.
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