linux-kernel - Re: [PATCH v5] clk: change clk_ops' ->determine

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Date:	Tue, 7 Jul 2015 17:57:48 -0700
From:	Stephen Boyd <sboyd@...eaurora.org>
To:	Boris Brezillon <boris.brezillon@...e-electrons.com>
Cc:	Mike Turquette <mturquette@...libre.com>,
	linux-clk@...r.kernel.org, Jonathan Corbet <corbet@....net>,
	Tony Lindgren <tony@...mide.com>,
	Ralf Baechle <ralf@...ux-mips.org>,
	Emilio López <emilio@...pez.com.ar>,
	Maxime Ripard <maxime.ripard@...e-electrons.com>,
	Tero Kristo <t-kristo@...com>,
	Peter De Schrijver <pdeschrijver@...dia.com>,
	Prashant Gaikwad <pgaikwad@...dia.com>,
	Stephen Warren <swarren@...dotorg.org>,
	Thierry Reding <thierry.reding@...il.com>,
	Alexandre Courbot <gnurou@...il.com>,
	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-omap@...r.kernel.org,
	linux-mips@...ux-mips.org, linux-tegra@...r.kernel.org
Subject: Re: [PATCH v5] clk: change clk_ops' ->determine_rate() prototype

On 07/07, Boris Brezillon wrote:
> Clock rates are stored in an unsigned long field, but ->determine_rate()
> (which returns a rounded rate from a requested one) returns a long
> value (errors are reported using negative error codes), which can lead
> to long overflow if the clock rate exceed 2Ghz.
> 
> Change ->determine_rate() prototype to return 0 or an error code, and pass
> a pointer to a clk_rate_request structure containing the expected target
> rate and the rate constraints imposed by clk users.
> 
> The clk_rate_request structure might be extended in the future to contain
> other kind of constraints like the rounding policy, the maximum clock
> inaccuracy or other things that are not yet supported by the CCF
> (power consumption constraints ?).
> 
> Signed-off-by: Boris Brezillon <boris.brezillon@...e-electrons.com>
> 
> CC: Jonathan Corbet <corbet@....net>
> CC: Tony Lindgren <tony@...mide.com>
> CC: Ralf Baechle <ralf@...ux-mips.org>
> CC: "Emilio López" <emilio@...pez.com.ar>
> CC: Maxime Ripard <maxime.ripard@...e-electrons.com>
> CC: Tero Kristo <t-kristo@...com>
> CC: Peter De Schrijver <pdeschrijver@...dia.com>
> CC: Prashant Gaikwad <pgaikwad@...dia.com>
> CC: Stephen Warren <swarren@...dotorg.org>
> CC: Thierry Reding <thierry.reding@...il.com>
> CC: Alexandre Courbot <gnurou@...il.com>
> CC: linux-doc@...r.kernel.org
> CC: linux-kernel@...r.kernel.org
> CC: linux-arm-kernel@...ts.infradead.org
> CC: linux-omap@...r.kernel.org
> CC: linux-mips@...ux-mips.org
> CC: linux-tegra@...r.kernel.org
> 
> ---

I'll throw this patch into -next now to see if any other problems
shake out. I'm hoping we get some more acks though, so it'll be
on it's own branch and become immutable in a week or so. One
question below.

> diff --git a/drivers/clk/clk-composite.c b/drivers/clk/clk-composite.c
> index 616f5ae..9e69f34 100644
> --- a/drivers/clk/clk-composite.c
> +++ b/drivers/clk/clk-composite.c
> @@ -99,33 +99,33 @@ static long clk_composite_determine_rate(struct clk_hw *hw, unsigned long rate,
>  
>  			parent_rate = __clk_get_rate(parent);
>  
> -			tmp_rate = rate_ops->round_rate(rate_hw, rate,
> +			tmp_rate = rate_ops->round_rate(rate_hw, req->rate,
>  							&parent_rate);
>  			if (tmp_rate < 0)
>  				continue;
>  
> -			rate_diff = abs(rate - tmp_rate);
> +			rate_diff = abs(req->rate - tmp_rate);
>  
> -			if (!rate_diff || !*best_parent_p
> +			if (!rate_diff || !req->best_parent_hw
>  				       || best_rate_diff > rate_diff) {
> -				*best_parent_p = __clk_get_hw(parent);
> -				*best_parent_rate = parent_rate;
> +				req->best_parent_hw = __clk_get_hw(parent);
> +				req->best_parent_rate = parent_rate;
>  				best_rate_diff = rate_diff;
>  				best_rate = tmp_rate;
>  			}
>  
>  			if (!rate_diff)
> -				return rate;
> +				return 0;
>  		}
>  
> -		return best_rate;
> +		req->rate = best_rate;
> +		return 0;
>  	} else if (mux_hw && mux_ops && mux_ops->determine_rate) {
>  		__clk_hw_set_clk(mux_hw, hw);
> -		return mux_ops->determine_rate(mux_hw, rate, min_rate,
> -					       max_rate, best_parent_rate,
> -					       best_parent_p);
> +		return mux_ops->determine_rate(mux_hw, req);
>  	} else {
>  		pr_err("clk: clk_composite_determine_rate function called, but no mux or rate callback set!\n");
> +		req->rate = 0;
>  		return 0;

Shouldn't this return an error now? And then assigning req->rate
wouldn't be necessary. Sorry I must have missed this last round.

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