Hi Stephen, On Tue, Jun 25, 2019 at 08:52:45PM -0700, Stephen Boyd wrote: > Quoting Weiyi Lu (2019-06-25 18:05:22) > > On Tue, 2019-06-25 at 15:14 -0700, Stephen Boyd wrote: > > > Quoting Weiyi Lu (2019-06-09 20:44:53) > > > > When using property assigned-clock-parents to assign parent clocks, > > > > core clocks might still be disabled during re-parent. > > > > Add flag 'CLK_OPS_CORE_ENABLE' for those clocks must be enabled > > > > during re-parent. > > > > > > > > Signed-off-by: Weiyi Lu <weiyi...@mediatek.com> > > > > > > Can you further describe the scenario where this is a problem? Is it > > > some sort of clk that is enabled by default out of the bootloader and is > > > then configured to have an 'assigned-clock-parents' property to change > > > the parent, but that clk needs to be "enabled" so that the framework > > > turns on the parents for the parent switch? > > > > When driver is built as module(.ko) and install at runtime after the > > whole initialization stage. Clk might already be turned off before > > configuring by assigned-clock-parents. For such clock design that need > > to have clock enabled during re-parent, the configuration of > > assigned-clock-parents might be failed. That's the problem we have now. > > Great. Please put this sort of information in the commit text. > > > Do you have any suggestion for such usage of clocks? Many thanks. > > Ok, and in this case somehow CLK_OPS_PARENT_ENABLE flag doesn't work? Is > that because the clk itself doesn't do anything unless it's enabled? I > seem to recall that we usually work around this by caching the state of > the clk parents or frequencies and then when the clk prepare or enable > op is called we actually write the hardware to change the state. There > are some qcom clks like this and we basically just use the hardware > itself to cache the state of the clk while it hasn't actually changed to > be at that rate, because the clk is not enabled yet.
I'm trying to move the fix to the clock driver itself. Do you have any pointer to such a clock that I can use as an example ? > The main concern is that we're having to turn on clks to make things > work, when it would be best to not turn on clks just so that register > writes actually make a difference to what the hardware does. I agree, it's best not to turn the clock on if we can avoid it. -- Regards, Laurent Pinchart