linux-kernel - Re: [PATCH v2] clk: Add clk_composite_set_rate_and

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Date:	Fri, 15 Apr 2016 15:15:28 -0700
From:	Stephen Boyd <sboyd@...eaurora.org>
To:	Finlye Xiao <finley.xiao@...k-chips.com>
Cc:	mturquette@...libre.com, heiko@...ech.de,
	linux-clk@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	linux-rockchip@...ts.infradead.org, zhengxing@...k-chips.com,
	wxt@...k-chips.com, zyw@...k-chips.com, jay.xu@...k-chips.com,
	zhangqing@...k-chips.com, xxx@...k-chips.com,
	huangtao@...k-chips.com
Subject: Re: [PATCH v2] clk: Add clk_composite_set_rate_and_parent

On 04/12, Finlye Xiao wrote:
> From: Finley Xiao <finley.xiao@...k-chips.com>
> 
> When changing the clock-rate, currently a new parent is set first and a
> divider adapted thereafter. This may result in the clock-rate overflowing
> its target rate for a short time if the new parent has a higher rate than
> the old parent.
> 
> While this often doesn't produce negative effects, it can affect components
> in a voltage-scaling environment, like the GPU on the rk3399 socs, where
> the voltage than simply is to low for the temporarily to high clock rate.
> 
> For general clock hirarchies this may need more extensive adaptions to
> the common clock-framework, but at least for composite clocks having
> both parent and rate settings it is easy to create a short-term solution to
> make sure the clock-rate does not overflow the target.
> 
> Signed-off-by: Finley Xiao <finley.xiao@...k-chips.com>
> Reviewed-by: Heiko Stuebner <heiko@...ech.de>
> ---

Applied to clk-next

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