linux-kernel - RE: [PATCH v2 06/17] clk: imx: pll14xx: use rate

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Date: Mon, 13 May 2024 11:56:39 +0000
From: Peng Fan <peng.fan@....com>
To: Rasmus Villemoes <rasmus.villemoes@...vas.dk>, "Peng Fan (OSS)"
	<peng.fan@....nxp.com>, Abel Vesa <abelvesa@...nel.org>, Michael Turquette
	<mturquette@...libre.com>, Stephen Boyd <sboyd@...nel.org>, Shawn Guo
	<shawnguo@...nel.org>, Sascha Hauer <s.hauer@...gutronix.de>, Pengutronix
 Kernel Team <kernel@...gutronix.de>, Fabio Estevam <festevam@...il.com>,
	Jacky Bai <ping.bai@....com>, Ye Li <ye.li@....com>, Aisheng Dong
	<aisheng.dong@....com>
CC: "linux-clk@...r.kernel.org" <linux-clk@...r.kernel.org>,
	"imx@...ts.linux.dev" <imx@...ts.linux.dev>,
	"linux-arm-kernel@...ts.infradead.org"
	<linux-arm-kernel@...ts.infradead.org>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>, Abel Vesa <abel.vesa@...aro.org>, "S.J. Wang"
	<shengjiu.wang@....com>
Subject: RE: [PATCH v2 06/17] clk: imx: pll14xx: use rate_table for audio plls

> Subject: Re: [PATCH v2 06/17] clk: imx: pll14xx: use rate_table for audio plls
> 
> On 10/05/2024 11.19, Peng Fan (OSS) wrote:
> > From: Shengjiu Wang <shengjiu.wang@....com>
> >
> > The generated clock frequency may not accurate, for example the
> > expected rate is 361267200U, but result is 361267199U.
> > Add rate_table for audio clocks to avoid such issue.
> >
> > Signed-off-by: Shengjiu Wang <shengjiu.wang@....com>
> > Reviewed-by: Jacky Bai <ping.bai@....com>
> > Signed-off-by: Peng Fan <peng.fan@....com>
> > ---
> >  drivers/clk/imx/clk-pll14xx.c | 11 +++++++++++
> >  1 file changed, 11 insertions(+)
> >
> > diff --git a/drivers/clk/imx/clk-pll14xx.c
> > b/drivers/clk/imx/clk-pll14xx.c index 55812bfb9ec2..6b2c849f8b71
> > 100644
> > --- a/drivers/clk/imx/clk-pll14xx.c
> > +++ b/drivers/clk/imx/clk-pll14xx.c
> > @@ -64,6 +64,17 @@ static const struct imx_pll14xx_rate_table
> imx_pll1443x_tbl[] = {
> >  	PLL_1443X_RATE(650000000U, 325, 3, 2, 0),
> >  	PLL_1443X_RATE(594000000U, 198, 2, 2, 0),
> >  	PLL_1443X_RATE(519750000U, 173, 2, 2, 16384),
> > +	PLL_1443X_RATE(393216000U, 262, 2, 3, 9437),
> > +	PLL_1443X_RATE(361267200U, 361, 3, 3, 17511),
> 
> Sorry, what? This reintroduces the two entries that were removed in
> 72d00e560d10, 

I overlooked this.

claiming that this produces an exact output, whereas that
> commit very clearly states (and it's easy to do the math and verify) that those
> entries actually resulted in output values of 393215995 and 361267196. So
> even if the dynamic computation would result in 361267199 (it doesn't, it
> gives an exact output), that would still be better than what these hard-coded
> entries achieve.
ok, I will let Shengjiu to comment on this.

Thanks
Peng.

> 
> Rasmus