linux-kernel - Re: [PATCH] clk: tegra: use pll_ref as the pll

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Date:	Wed, 30 Oct 2013 16:44:10 +0100
From:	Lucas Stach <l.stach@...gutronix.de>
To:	Stephen Warren <swarren@...dotorg.org>
Cc:	Peter De Schrijver <pdeschrijver@...dia.com>,
	Prashant Gaikwad <pgaikwad@...dia.com>,
	Mike Turquette <mturquette@...aro.org>,
	Mark Zhang <markz@...dia.com>, linux-kernel@...r.kernel.org,
	linux-tegra@...r.kernel.org, Thierry Reding <treding@...dia.com>,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] clk: tegra: use pll_ref as the pll_e parent

Am Mittwoch, den 30.10.2013, 09:41 -0600 schrieb Stephen Warren:
> On 10/29/2013 06:41 PM, Peter De Schrijver wrote:
> > Use pll_ref instead of pll_re_vco as the pll_e parent on Tegra114 and
> > Tegra124. Also add a pll_ref table entry for pll_e for Tegra114.
> 
> Why? What benefit does this give, or what bug does this fix?
> 
> > diff --git a/drivers/clk/tegra/clk-pll.c b/drivers/clk/tegra/clk-pll.c
> 
> >  	val_aux = pll_readl(pll_params->aux_reg, pll);
> >  
> >  	if (val & PLL_BASE_ENABLE) {
> > -		if (!(val_aux & PLLE_AUX_PLLRE_SEL))
> > +		if ((val_aux & PLLE_AUX_PLLRE_SEL) || (val_aux & val_aux))
> 
> Isn't "|| (val_aux & val_aux)" always true, at least if the value is
> non-zero? Either this should be simply "|| val_aux", or one of those two
> "val_aux" is the wrong thing.
> 
> >  			WARN(1, "pll_e enabled with unsupported parent %s\n",
> > -			  (val & PLLE_AUX_PLLP_SEL) ? "pllp_out0" : "pll_ref");
> > +			  (val_aux & PLLE_AUX_PLLP_SEL) ? "pllp_out0" :
> > +					"pll_re_vco");
> >  	} else {
> > -		val_aux |= PLLE_AUX_PLLRE_SEL;
> > +		val_aux &= ~(PLLE_AUX_PLLRE_SEL | PLLE_AUX_PLLP_SEL);
> >  		pll_writel(val, pll_params->aux_reg, pll);
> >  	}
> 
> > diff --git a/drivers/clk/tegra/clk-tegra114.c b/drivers/clk/tegra/clk-tegra114.c
> 
> > @@ -560,6 +560,7 @@ static struct tegra_clk_pll_freq_table pll_e_freq_table[] = {
> >  	/* PLLE special case: use cpcon field to store cml divider value */
> >  	{336000000, 100000000, 100, 21, 16, 11},
> >  	{312000000, 100000000, 200, 26, 24, 13},
> > +	{12000000, 100000000, 200,  1,  24, 13},
> 
> Presumably this is because pll_ref is the crystal, which runs at 12MHz.
> What if it doesn't; Tegra supports a bunch of other crystal rates. Don't
> we need entries for all the other potential crystal rates too?

The TRM states that PCIe and thus PLLE are only supported with 12MHz
external crystal rate.

-- 
Pengutronix e.K.                           | Lucas Stach                 |
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