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

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Date:	Fri, 24 Jun 2016 16:52:42 -0700
From:	Michael Turquette <mturquette@...libre.com>
To:	Dong Aisheng <aisheng.dong@....com>, linux-clk@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, sboyd@...eaurora.org,
	shawnguo@...nel.org, linux-arm-kernel@...ts.infradead.org,
	aisheng.dong@....com, anson.huang@....com
Subject: Re: [RESEND PATCH 3/8] clk: core: support clocks which requires parents on
 (part 1)

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 <mturquette@...libre.com>
> Cc: Stephen Boyd <sboyd@...eaurora.org>
> Cc: Shawn Guo <shawnguo@...nel.org>
> Signed-off-by: Dong Aisheng <aisheng.dong@....com>
> ---
>  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?

Regards,
Mike

>  
>  struct clk;
>  struct clk_hw;
> -- 
> 1.9.1
>