linux-kernel - Re: [PATCH v2 1/2] clk: change clk_ops' ->round

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Message-ID: <alpine.DEB.2.02.1506042258530.12316@utopia.booyaka.com>
Date:	Thu, 4 Jun 2015 23:02:25 +0000 (UTC)
From:	Paul Walmsley <paul@...an.com>
To:	Boris Brezillon <boris.brezillon@...e-electrons.com>
cc:	Mike Turquette <mturquette@...aro.org>,
	Stephen Boyd <sboyd@...eaurora.org>, linux-clk@...r.kernel.org,
	linux-kernel@...r.kernel.org, Jonathan Corbet <corbet@....net>,
	Shawn Guo <shawn.guo@...aro.org>,
	ascha Hauer <kernel@...gutronix.de>,
	David Brown <davidb@...eaurora.org>,
	Daniel Walker <dwalker@...o99.com>,
	Bryan Huntsman <bryanh@...eaurora.org>,
	Tony Lindgren <tony@...mide.com>,
	Liviu Dudau <liviu.dudau@....com>,
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Subject: Re: [PATCH v2 1/2] clk: change clk_ops' ->round_rate() prototype

Hi folks

just a brief comment on this one:

On Thu, 30 Apr 2015, Boris Brezillon wrote:

> Clock rates are stored in an unsigned long field, but ->round_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 ->round_rate() prototype to return 0 or an error code, and pass the
> requested rate as a pointer so that it can be adjusted depending on
> hardware capabilities.

...

> diff --git a/Documentation/clk.txt b/Documentation/clk.txt
> index 0e4f90a..fca8b7a 100644
> --- a/Documentation/clk.txt
> +++ b/Documentation/clk.txt
> @@ -68,8 +68,8 @@ the operations defined in clk.h:
>  		int		(*is_enabled)(struct clk_hw *hw);
>  		unsigned long	(*recalc_rate)(struct clk_hw *hw,
>  						unsigned long parent_rate);
> -		long		(*round_rate)(struct clk_hw *hw,
> -						unsigned long rate,
> +		int		(*round_rate)(struct clk_hw *hw,
> +						unsigned long *rate,
>  						unsigned long *parent_rate);
>  		long		(*determine_rate)(struct clk_hw *hw,
>  						unsigned long rate,

I'd suggest that we should probably go straight to 64-bit rates.  There 
are already plenty of clock sources that can generate rates higher than 
4GiHz.


- Paul
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