Re: [PATCH V2] clk: Add composite clock type

[Prashant Gaikwad]

On Wednesday 13 March 2013 10:00 PM, Tomasz Figa wrote:
> Hi Prashant,
>
> On Thursday 28 of February 2013 11:20:31 Stephen Warren wrote:
> > On 02/28/2013 12:58 AM, Prashant Gaikwad wrote:
> > > On Wednesday 06 February 2013 03:36 PM, Tomasz Figa wrote:
> > > > On Wednesday 06 of February 2013 08:34:32 Prashant Gaikwad wrote:
> > > > > On Tuesday 05 February 2013 03:45 PM, Tomasz Figa wrote:
> > > > > > Hi Prashant,
> > > > > >
> > > > > > Thank you for your patch. Please see some comments inline.
> > > > > >
> > > > > > On Monday 04 of February 2013 13:41:22 Prashant Gaikwad wrote:
> > > > > > > Not all clocks are required to be decomposed into basic clock
> > > > > > > types but at the same time want to use the functionality
> > > > > > > provided by these basic clock types instead of duplicating.
> > > > > > >
> > > > > > > For example, Tegra SoC has ~100 clocks which can be decomposed
> > > > > > > into Mux -> Div -> Gate clock types making the clock count to
> > > > > > > ~300. Also, parent change operation can not be performed on gate
> > > > > > > clock which forces to use mux clock in driver if want to change
> > > > > > > the parent.
> > > > > > >
> > > > > > > Instead aggregate the basic clock types functionality into one
> > > > > > > clock and just use this clock for all operations. This clock
> > > > > > > type re-uses the functionality of basic clock types and not
> > > > > > > limited to basic clock types but any hardware-specific
> > > > > > > implementation.
> > > > > > >
> > > > > > > diff --git a/drivers/clk/clk-composite.c
> > > > > > >
> > > > > > > +static u8 clk_composite_get_parent(struct clk_hw *hw)
> > > > > > > +{
> > > > > > > +     struct clk_composite *composite = to_clk_composite(hw);
> > > > > > > +     const struct clk_ops *mux_ops = composite->mux_ops;
> > > > > > > +     struct clk_hw *mux_hw = composite->mux_hw;
> > > > > > > +
> > > > > > > +     mux_hw->clk = hw->clk;
> > > > > > Why is this needed? Looks like this filed is already being initialized
> > > > > > in clk_register_composite.
> > > > > Some ops will get called during clk_init where this clk is not populated
> > > > > hence doing here. I have done it for all ops to make sure that any
> > > > > future change in clock framework don't break this clock.
> > > > > Now, why duplicate it in clk_register_composite? It is possible that
> > > > > none of these ops get called in clk_init.
> > > > > For example, recalc_rate is called during init and this ops is supported
> > > > > by div clock type, but what if div clock is not added.
> > > > >
> > > > > I hope this explains the need.
> > > > Sorry, I don't understand your explanation.
> > > >
> > > > I have asked why mux_hw->clk field has to be reinitialized in all the
> > > > ops.
> > > >
> > > > In other words, is it even possible that this clk pointer changes since
> > > > calling clk_register from clk_register_composite and if yes, why?
> > > Tomasz,
> > >
> > > calling sequence is as
> > >
> > > clk_register(struct clk_hw *hw)
> > >
> > >      clk_init(struct clk_hw *hw)
> > >      
> > >          .
> > >          .
> > >          hw->clk = clk;
> > >          clk->ops.recalc_rate(hw) => clk_composite_recalc_rate(hw) =>
> > >
> > > composite->div_ops.recalc_rate(div_hw) => clk_divider_recalc_rate(hw)
> > >
> > > Now if clk_divider_recalc_rate tries to access clk from hw then it will
> > > get NULL since this is not assigned yet and that is what I am doing in
> > > clk_composite_recalc_rate.
> > >
> > > I am doing it in all ops because I can not assume which one will get
> > > called first and always. If in future something changes the calling
> > > sequence in ccf framework then it will break this clock.
> > Surely the CCF core should be taking care of this as part of
> > clk_register() or clk_init()?
> Any news on this? It would be nice if this patch could be merged soon, because
> we'd like to rework Exynos clock code to use composite clocks before merge
> window, to have that merged for 3.10.
>
> If you don't have time to work on this, would you mind if I made any necessary
> fixes, added my sign-off next to yours and posted next version myself?

Tomasz,

Sorry for delayed reply. I will send the updated patch in next 2-3 days. 
After that if any rework required you can make the changes and add your 
sign-off.

Thanks for the patience!!

Regards,
PrashantG

> Best regards,

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