linux-kernel - Re: [PATCH v11 3/4] clk: Add rate constraints to clocks

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Message-ID: <20150122014635.GI27202@codeaurora.org>
Date:	Wed, 21 Jan 2015 17:46:35 -0800
From:	Stephen Boyd <sboyd@...eaurora.org>
To:	Tomeu Vizoso <tomeu.vizoso@...labora.com>
Cc:	linux-kernel@...r.kernel.org,
	Mike Turquette <mturquette@...aro.org>,
	Javier Martinez Canillas <javier.martinez@...labora.co.uk>,
	Jonathan Corbet <corbet@....net>,
	Tony Lindgren <tony@...mide.com>,
	Russell King <linux@....linux.org.uk>,
	Ralf Baechle <ralf@...ux-mips.org>,
	Boris Brezillon <boris.brezillon@...e-electrons.com>,
	Emilio López <emilio@...pez.com.ar>,
	Maxime Ripard <maxime.ripard@...e-electrons.com>,
	Tero Kristo <t-kristo@...com>,
	Manuel Lauss <manuel.lauss@...il.com>,
	Alex Elder <elder@...aro.org>,
	Matt Porter <mporter@...aro.org>,
	Zhangfei Gao <zhangfei.gao@...aro.org>,
	Haojian Zhuang <haojian.zhuang@...aro.org>,
	Jaehoon Chung <jh80.chung@...sung.com>,
	Bintian Wang <bintian.wang@...wei.com>,
	Chao Xie <chao.xie@...vell.com>, linux-doc@...r.kernel.org,
	linux-omap@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linux-mips@...ux-mips.org
Subject: Re: [PATCH v11 3/4] clk: Add rate constraints to clocks

On 01/21, Tomeu Vizoso wrote:
> Adds a way for clock consumers to set maximum and minimum rates. This
> can be used for thermal drivers to set minimum rates, or by misc.
> drivers to set maximum rates to assure a minimum performance level.
> 
> Changes the signature of the determine_rate callback by adding the
> parameters min_rate and max_rate.
> 
> Signed-off-by: Tomeu Vizoso <tomeu.vizoso@...labora.com>
> 
> ---
> v11:	* Recalculate the rate before putting the reference to clk_core
> 	* Don't recalculate the rate when freeing the per-user clock
> 	in the initialization error paths
> 	* Move __clk_create_clk to be next to __clk_free_clk for more
> 	comfortable reading

Can we do this in the previous patch where we introduce the
function?

> @@ -2143,9 +2314,16 @@ struct clk *__clk_register(struct device *dev, struct clk_hw *hw)
>  	else
>  		clk->owner = NULL;
>  
> +	INIT_HLIST_HEAD(&clk->clks);
> +
> +	hw->clk = __clk_create_clk(hw, NULL, NULL);
> +
>  	ret = __clk_init(dev, hw->clk);
> -	if (ret)
> +	if (ret) {
> +		__clk_free_clk(hw->clk);
> +		hw->clk = NULL;
>  		return ERR_PTR(ret);
> +	}
>  
>  	return hw->clk;
>  }
> @@ -2210,12 +2388,16 @@ struct clk *clk_register(struct device *dev, struct clk_hw *hw)
>  		}
>  	}
>  
> +	INIT_HLIST_HEAD(&clk->clks);
> +
>  	hw->clk = __clk_create_clk(hw, NULL, NULL);
>  	ret = __clk_init(dev, hw->clk);
>  	if (!ret)
>  		return hw->clk;
>  
> -	kfree(hw->clk);
> +	__clk_free_clk(hw->clk);
> +	hw->clk = NULL;

Shouldn't we be assigning to NULL in the previous patch (same
comment for __clk_register)?

>  fail_parent_names_copy:
>  	while (--i >= 0)
>  		kfree(clk->parent_names[i]);
> @@ -2420,7 +2602,14 @@ void __clk_put(struct clk *clk)
>  	if (!clk || WARN_ON_ONCE(IS_ERR(clk)))
>  		return;
>  
> +	clk_prepare_lock();
> +	hlist_del(&clk->child_node);
> +	clk_prepare_unlock();
> +
> +	clk_core_set_rate(clk->core, clk->core->req_rate);
> +
>  	clk_core_put(clk->core);
> +

Sad that we take the lock 3 times during __clk_put(). We should
be able to do it only once if we have a lockless
clk_core_set_rate() function and put the contents of
clk_core_put() into this function. Actually we need to do that to
be thread safe with clk->core->req_rate changing. We can call the
same function in clk_set_rate_range() too so that we don't have
to deal with recursive locking there.

>  	kfree(clk);
>  }
>  

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