linux-kernel - Re: [PATCH 02/11] clk: imx: correct AV PLL rate formula

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Message-ID: <20160612113016.GZ20243@tiger>
Date:	Sun, 12 Jun 2016 19:30:16 +0800
From:	Shawn Guo <shawnguo@...nel.org>
To:	Dong Aisheng <aisheng.dong@....com>
Cc:	linux-clk@...r.kernel.org, anson.huang@....com,
	mturquette@...libre.com, sboyd@...eaurora.org,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 02/11] clk: imx: correct AV PLL rate formula

On Wed, Jun 08, 2016 at 10:33:31PM +0800, Dong Aisheng wrote:
> From: Anson Huang <b20788@...escale.com>
> 
> The audio/video PLL's rate calculation is as below in RM:
> 
> Fref * (DIV_SELECT + NUM / DENOM), in origin clk-pllv3's
> code, below code is used:
> 
> (parent_rate * div) + ((parent_rate / mfd) * mfn
> 
> as it does NOT consider the float data using div, so below
> formula should be used as a decent method:
> 
> (parent_rate * div) + ((parent_rate * mfn) / mfd)
> 
> and we also need to consider parent_rate * mfd may overflow
> a 32 bit value, 64 bit value should be used.
> 
> After updating this formula, the dram PLL's rate is
> 1066MHz, which is correct, while the old formula gets
> 1056MHz.
> 
> [Aisheng: fix clk_pllv3_av_round_rate too]
> 
> Signed-off-by: Anson Huang <b20788@...escale.com>
> Signed-off-by: Dong Aisheng <aisheng.dong@....com>

Applied, thanks.