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

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Message-ID: <527128B5.2020101@wwwdotorg.org>
Date:	Wed, 30 Oct 2013 09:41:41 -0600
From:	Stephen Warren <swarren@...dotorg.org>
To:	Peter De Schrijver <pdeschrijver@...dia.com>
CC:	Mike Turquette <mturquette@...aro.org>,
	Prashant Gaikwad <pgaikwad@...dia.com>,
	Mark Zhang <markz@...dia.com>,
	Thierry Reding <treding@...dia.com>,
	linux-arm-kernel@...ts.infradead.org, linux-tegra@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] clk: tegra: use pll_ref as the pll_e parent

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?
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