linux-kernel - Re: [PATCH] clk: Only recalculate the rate if needed

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Date:	Thu, 19 Feb 2015 19:29:41 -0800
From:	Mike Turquette <mturquette@...aro.org>
To:	Tomeu Vizoso <tomeu.vizoso@...labora.com>,
	linux-kernel@...r.kernel.org
Cc:	"Javier Martinez Canillas" <javier.martinez@...labora.co.uk>,
	"Tomeu Vizoso" <tomeu.vizoso@...labora.com>,
	"Thierry Reding" <thierry.reding@...il.com>,
	"Peter De Schrijver" <pdeschrijver@...dia.com>,
	"Stephen Boyd" <sboyd@...eaurora.org>
Subject: Re: [PATCH] clk: Only recalculate the rate if needed

Quoting Tomeu Vizoso (2015-02-06 06:13:01)
> We don't really need to recalculate the effective rate of a clock when a
> per-user clock is removed, if the constraints of the later aren't
> limiting the requested rate.
> 
> This was causing problems with clocks that never had a rate set before,
> as rate_req would be zero. Though this could be considered a bug in the
> implementation of those clocks, this should be checked somewhere else.
> 
> Cc: Thierry Reding <thierry.reding@...il.com>
> Cc: Peter De Schrijver <pdeschrijver@...dia.com>
> Signed-off-by: Tomeu Vizoso <tomeu.vizoso@...labora.com>

Fixes: 1c8e600440c7 ("clk: Add rate constraints to clocks")

Applied to clk-next. With this fix sunxi no longer vomits WARNs
everywhere due to divide-by-zero in the following path:

of_clk_init -> parent_ready -> __clk_put

Thanks,
Mike

> 
> ---
> 
> This applies on top of https://lkml.org/lkml/2015/2/5/769
> ---
>  drivers/clk/clk.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
> index a7d37c3..4ea2d53 100644
> --- a/drivers/clk/clk.c
> +++ b/drivers/clk/clk.c
> @@ -2664,7 +2664,11 @@ void __clk_put(struct clk *clk)
>         clk_prepare_lock();
>  
>         hlist_del(&clk->clks_node);
> -       clk_core_set_rate_nolock(clk->core, clk->core->req_rate);
> +
> +       if (clk->min_rate > clk->core->req_rate ||
> +           clk->max_rate < clk->core->req_rate)
> +               clk_core_set_rate_nolock(clk->core, clk->core->req_rate);
> +
>         owner = clk->core->owner;
>         kref_put(&clk->core->ref, __clk_release);
>  
> -- 
> 1.9.3
> 
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