Subject: [RESEND PATCH 3/8] clk: core: support clocks which requires parents on (part 1)

From: [email-masked] (Dong Aisheng)
Date: Wed, 29 Jun 2016 21:57:09 +0800

On Fri, Jun 24, 2016 at 04:52:42PM -0700, Michael Turquette wrote:
> Quoting Dong Aisheng (2016-04-20 02:34:35)
> > On Freescale i.MX7D platform, all clocks operations, including
> > enable/disable, rate change and re-parent, requires its parent
> > clock on. Current clock core can not support it well.
> > This patch introduce a new flag CLK_OPS_PARENT_ON to handle this
> > special case in clock core that enable its parent clock firstly for
> > each operation and disable it later after operation complete.
> > 
> > The patch part 1 fixes the possible disabling clocks while its parent
> > is off during kernel booting phase in clk_disable_unused_subtree().
> > 
> > Before the completion of kernel booting, clock tree is still not built
> > completely, there may be a case that the child clock is on but its
> > parent is off which could be caused by either HW initial reset state
> > or bootloader initialization.
> > 
> > Taking bootloader as an example, we may enable all clocks in HW by default.
> > And during kernel booting time, the parent clock could be disabled in its
> > driver probe due to calling clk_prepare_enable and clk_disable_unprepare.
> > Because it's child clock is only enabled in HW while its SW usecount
> > in clock tree is still 0, so clk_disable of parent clock will gate
> > the parent clock in both HW and SW usecount ultimately. Then there will
> > be a child clock is still on in HW but its parent is already off.
> > 
> > Later in clk_disable_unused(), this clock disable accessing while its
> > parent off will cause system hang due to the limitation of HW which
> > must require its parent on.
> > 
> > This patch simply enables the parent clock first before disabling
> > if flag CLK_OPS_PARENT_ON is set in clk_disable_unused_subtree().
> > This is a simple solution and only affects booting time.
> > 
> > After kernel booting up the clock tree is already created, there will
> > be no case that child is off but its parent is off.
> > So no need do this checking for normal clk_disable() later.
> > 
> > Cc: Michael Turquette <[email-masked]>
> > Cc: Stephen Boyd <[email-masked]>
> > Cc: Shawn Guo <[email-masked]>
> > Signed-off-by: Dong Aisheng <[email-masked]>
> > ---
> >  drivers/clk/clk.c            | 5 +++++
> >  include/linux/clk-provider.h | 2 ++
> >  2 files changed, 7 insertions(+)
> > 
> > diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
> > index 9f944d4..1f054d1a 100644
> > --- a/drivers/clk/clk.c
> > +++ b/drivers/clk/clk.c
> > @@ -765,6 +765,9 @@ static void clk_disable_unused_subtree(struct clk_core *core)
> >         hlist_for_each_entry(child, &core->children, child_node)
> >                 clk_disable_unused_subtree(child);
> >  
> > +       if (core->flags & CLK_OPS_PARENT_ON)
> > +               clk_core_prepare_enable(core->parent);
> > +
> >         flags = clk_enable_lock();
> >  
> >         if (core->enable_count)
> > @@ -789,6 +792,8 @@ static void clk_disable_unused_subtree(struct clk_core *core)
> >  
> >  unlock_out:
> >         clk_enable_unlock(flags);
> > +       if (core->flags & CLK_OPS_PARENT_ON)
> > +               clk_core_disable_unprepare(core->parent);
> >  }
> >  
> >  static bool clk_ignore_unused;
> > diff --git a/include/linux/clk-provider.h b/include/linux/clk-provider.h
> > index 15628644..c878f9c 100644
> > --- a/include/linux/clk-provider.h
> > +++ b/include/linux/clk-provider.h
> > @@ -33,6 +33,8 @@
> >  #define CLK_RECALC_NEW_RATES   BIT(9) /* recalc rates after notifications */
> >  #define CLK_SET_RATE_UNGATE    BIT(10) /* clock needs to run to set rate */
> >  #define CLK_IS_CRITICAL                BIT(11) /* do not gate, ever */
> > +/* parents need on during gate/ungate, set rate and re-parent */
> > +#define CLK_OPS_PARENT_ON      BIT(12)
> 
> Hi Dong,
> 
> In the clk framework we use "enabled" instead of "on". How about
> changing the flag to CLK_OPS_PARENT_ENABLE?
> 

Yes, of course i'm fine with it.
I could update the patch title too.
Thanks for the review.

Regards
Dong Aisheng

> Regards,
> Mike
> 
> >  
> >  struct clk;
> >  struct clk_hw;
> > -- 
> > 1.9.1
> > 
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