linux-kernel - Re: [PATCH] ARC: [plat-hsdk]: Temporary fix to set CPU frequency to 1GHz

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Message-ID: <1506711271.3461.7.camel@synopsys.com>
Date:   Fri, 29 Sep 2017 18:54:31 +0000
From:   Eugeniy Paltsev <Eugeniy.Paltsev@...opsys.com>
To:     "Eugeniy.Paltsev@...opsys.com" <Eugeniy.Paltsev@...opsys.com>,
        "Vineet Gupta" <Vineet.Gupta1@...opsys.com>,
        "linux-snps-arc@...ts.infradead.org" 
        <linux-snps-arc@...ts.infradead.org>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Vineet.Gupta1@...opsys.com" <Vineet.Gupta1@...opsys.com>,
        "Alexey.Brodkin@...opsys.com" <Alexey.Brodkin@...opsys.com>
Subject: Re: [PATCH] ARC: [plat-hsdk]: Temporary fix to set CPU frequency to
 1GHz

On Fri, 2017-09-29 at 11:34 -0700, Vineet Gupta wrote:
> On 09/28/2017 07:33 AM, Eugeniy Paltsev wrote:
> > Add temporary fix to HSDK platform code to setup CPU frequency
> > to 1GHz on early boot.
> > We can remove this fix when smart hsdk pll driver will be
> > introduced, see discussion:
> > https://www.mail-archive.com/linux-snps-arc@lists.infradead.org/msg02689.html
> > 
> > Signed-off-by: Eugeniy Paltsev <Eugeniy.Paltsev@...opsys.com>
> > ---
> >   arch/arc/plat-hsdk/platform.c | 42 ++++++++++++++++++++++++++++++++++++++++++
> >   1 file changed, 42 insertions(+)
> > 
> > diff --git a/arch/arc/plat-hsdk/platform.c b/arch/arc/plat-hsdk/platform.c
> > index a2e7fd1..744e62e 100644
> > --- a/arch/arc/plat-hsdk/platform.c
> > +++ b/arch/arc/plat-hsdk/platform.c
> > @@ -38,6 +38,42 @@ static void __init hsdk_init_per_cpu(unsigned int cpu)
> >   #define CREG_PAE		(CREG_BASE + 0x180)
> >   #define CREG_PAE_UPDATE		(CREG_BASE + 0x194)
> >   
> > +#define CREG_CORE_IF_CLK_DIV	(CREG_BASE + 0x4B8)
> > +#define CREG_CORE_IF_CLK_DIV_2	0x1
> > +#define CGU_BASE		ARC_PERIPHERAL_BASE
> > +#define CGU_PLL_STATUS		(ARC_PERIPHERAL_BASE + 0x4)
> > +#define CGU_PLL_CTRL		(ARC_PERIPHERAL_BASE + 0x0)
> > +#define CGU_PLL_STATUS_LOCK	BIT(0)
> > +#define CGU_PLL_STATUS_ERR	BIT(1)
> > +#define CGU_PLL_CTRL_1GHZ	0x3A10
> > +#define HSDK_PLL_LOCK_TIMEOUT	500
> > +
> > +#define HSDK_PLL_LOCKED() \
> > +	!!(ioread32((void __iomem *) CGU_PLL_STATUS) & CGU_PLL_STATUS_LOCK)
> > +
> > +#define HSDK_PLL_ERR() \
> > +	!!(ioread32((void __iomem *) CGU_PLL_STATUS) & CGU_PLL_STATUS_ERR)
> > +
> > +static void __init hsdk_set_cpu_freq_1ghz(void)
> > +{
> > +	u32 timeout = HSDK_PLL_LOCK_TIMEOUT;
> > +
> > +	/*
> > +	 * As we set cpu clock which exceeds 500MHz, the divider for the interface
> > +	 * clock must be programmed to div-by-2.
> > +	 */
> > +	iowrite32(CREG_CORE_IF_CLK_DIV_2, (void __iomem *) CREG_CORE_IF_CLK_DIV);
> > +
> > +	/* Set cpu clock to 1GHz */
> > +	iowrite32(CGU_PLL_CTRL_1GHZ, (void __iomem *) CGU_PLL_CTRL);
> > +
> > +	while (!HSDK_PLL_LOCKED() && timeout--)
> > +		cpu_relax();
> > +
> > +	if (!HSDK_PLL_LOCKED() || HSDK_PLL_ERR())
> > +		pr_err("Failed to setup CPU frequency to 1GHz!");
> > +}
> > +
> >   static void __init hsdk_init_early(void)
> >   {
> >   	/*
> > @@ -52,6 +88,12 @@ static void __init hsdk_init_early(void)
> >   
> >   	/* Really apply settings made above */
> >   	writel(1, (void __iomem *) CREG_PAE_UPDATE);
> > +
> > +	/*
> > +	 * Setup CPU frequency to 1GHz.
> > +	 * TODO: remove it after smart hsdk pll driver will be introduced.
> > +	 */
> > +	hsdk_set_cpu_freq_1ghz();
> >   }
> 
> While this suffices our needs in the interim, is there a way to invoke the 
> existing clk driver to achieve the same results ?

There is only one place where we can add call of existing clk driver to set
cpu frequency.
It is in time_init function between early clock initialising and clocksource timer
probing:

------------------arch/arc/kernel/setup.c--------------------------
/*
 * Called from start_kernel() - boot CPU only
 */
void __init time_init(void)
{
	of_clk_init(NULL);
	                      /*  <--- We can add it here. */
	timer_probe();
}
--------------------------->8--------------------------------------

It will be look like that:
https://www.mail-archive.com/linux-snps-arc@lists.infradead.org/msg02587.html


> >   
> >   static const char *hsdk_compat[] __initconst = {
> > 
> 
> 
-- 
 Eugeniy Paltsev