Re: [RESEND PATCH 4/8] clk: core: support clocks which requires parents on (part 2)

[Michael Turquette]

Hi Dong,

Quoting Dong Aisheng (2016-04-20 02:34:36)
> 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 adding 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 2 fixes set clock rate and set parent while its parent
> is off. The most special case is for set_parent() operation which requires
> all parents including both old and new one to be enabled at the same time
> during the operation.
> 
> Cc: Michael Turquette <mturquette@xxxxxxxxxxxx>
> Cc: Stephen Boyd <sboyd@xxxxxxxxxxxxxx>
> Cc: Shawn Guo <shawnguo@xxxxxxxxxx>
> Signed-off-by: Dong Aisheng <aisheng.dong@xxxxxxx>
> ---
>  drivers/clk/clk.c | 45 ++++++++++++++++++++++++++++-----------------
>  1 file changed, 28 insertions(+), 17 deletions(-)
> 
> diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
> index 1f054d1a..d6cef61 100644
> --- a/drivers/clk/clk.c
> +++ b/drivers/clk/clk.c
> @@ -1174,7 +1174,7 @@ static struct clk_core *__clk_set_parent_before(struct clk_core *core,
>         struct clk_core *old_parent = core->parent;
>  
>         /*
> -        * Migrate prepare state between parents and prevent race with
> +        * 1. Migrate prepare state between parents and prevent race with
>          * clk_enable().
>          *
>          * If the clock is not prepared, then a race with
> @@ -1189,13 +1189,16 @@ static struct clk_core *__clk_set_parent_before(struct clk_core *core,
>          * hardware and software states.
>          *
>          * See also: Comment for clk_set_parent() below.
> +        *
> +        * 2. enable parent clocks for CLK_OPS_PARENT_ON clock
>          */
> -       if (core->prepare_count) {
> -               clk_core_prepare(parent);
> -               flags = clk_enable_lock();
> -               clk_core_enable(parent);
> -               clk_core_enable(core);
> -               clk_enable_unlock(flags);
> +       if (core->prepare_count || core->flags & CLK_OPS_PARENT_ON) {
> +               clk_core_prepare_enable(parent);
> +               if (core->prepare_count)
> +                       clk_core_enable_lock(core);
> +               else
> +                       clk_core_prepare_enable(old_parent);

It took me a few seconds to figure out what I was looking at. The
set_parent stuff is tricky enough already ... I think we should keep the
state machine logic very simple. How about:

	/* enable old_parent & parent if CLK_OPS_PARENT_ENABLE is set */
	if (core->flags & CLK_OPS_PARENT_ENABLE) {
		clk_core_prepare_enable(old_parent);
		clk_core_prepare_enable(parent);
	}

	/* migrate prepare count if > 0 */
	if (core->prepare_count) {
		clk_core_prepare_enable(parent);
		clk_core_enable_lock(core);
	}

> +
>         }
>  
>         /* update the clk tree topology */
> @@ -1210,18 +1213,16 @@ static void __clk_set_parent_after(struct clk_core *core,
>                                    struct clk_core *parent,
>                                    struct clk_core *old_parent)
>  {
> -       unsigned long flags;
> -
>         /*
>          * Finish the migration of prepare state and undo the changes done
>          * for preventing a race with clk_enable().
>          */
> -       if (core->prepare_count) {
> -               flags = clk_enable_lock();
> -               clk_core_disable(core);
> -               clk_core_disable(old_parent);
> -               clk_enable_unlock(flags);
> -               clk_core_unprepare(old_parent);
> +       if (core->prepare_count || core->flags & CLK_OPS_PARENT_ON) {
> +               clk_core_disable_unprepare(old_parent);
> +               if (core->prepare_count)
> +                       clk_core_disable_lock(core);
> +               else
> +                       clk_core_disable_unprepare(parent);

Similarly, a more readable solution is:

	/*
	 * Finish the migration of prepare state and undo the changes done
	 * for preventing a race with clk_enable().
	 */
	if (core->prepare_count) {
		clk_core_disable_lock(core);
		clk_core_disable_unprepare(old_parent);

	/* re-balance ref counting if CLK_OPS_PARENT_ENABLE is set */
	if (core->flags & CLK_OPS_PARENT_ENABLE) {
		clk_core_disable_unprepare(parent);
		clk_core_disable_unprepare(old_parent);
	}

>         }
>  }
>  
> @@ -1468,13 +1469,17 @@ static void clk_change_rate(struct clk_core *core)
>         unsigned long best_parent_rate = 0;
>         bool skip_set_rate = false;
>         struct clk_core *old_parent;
> +       struct clk_core *parent = NULL;
>  
>         old_rate = core->rate;
>  
> -       if (core->new_parent)
> +       if (core->new_parent) {
> +               parent = core->new_parent;
>                 best_parent_rate = core->new_parent->rate;
> -       else if (core->parent)
> +       } else if (core->parent) {
> +               parent = core->parent;
>                 best_parent_rate = core->parent->rate;
> +       }
>  
>         if (core->flags & CLK_SET_RATE_UNGATE) {
>                 unsigned long flags;
> @@ -1504,6 +1509,9 @@ static void clk_change_rate(struct clk_core *core)
>  
>         trace_clk_set_rate(core, core->new_rate);
>  
> +       if (core->flags & CLK_OPS_PARENT_ON)
> +               clk_core_prepare_enable(parent);
> +
>         if (!skip_set_rate && core->ops->set_rate)
>                 core->ops->set_rate(core->hw, core->new_rate, best_parent_rate);
>  
> @@ -1520,6 +1528,9 @@ static void clk_change_rate(struct clk_core *core)
>                 clk_core_unprepare(core);
>         }
>  
> +       if (core->flags & CLK_OPS_PARENT_ON)
> +               clk_core_disable_unprepare(parent);
> +

This part looks good to me.

Regards,
Mike

>         if (core->notifier_count && old_rate != core->rate)
>                 __clk_notify(core, POST_RATE_CHANGE, old_rate, core->rate);
>  
> -- 
> 1.9.1
>