[U-Boot] [PATCH 2/2] ARM: tegra114: Clear IDDQ when enabling PLLC

[Thierry Reding]

On Tue, Sep 08, 2015 at 03:58:38PM +0000, Tom Warren wrote:
> Thierry,
> 
> > -----Original Message-----
> > From: Thierry Reding [mailto:thierry.reding at gmail.com]
> > Sent: Tuesday, September 08, 2015 2:38 AM
> > To: Tom Warren
> > Cc: Nicolas Chauvet; u-boot at lists.denx.de
> > Subject: [PATCH 2/2] ARM: tegra114: Clear IDDQ when enabling PLLC
> > 
> > From: Thierry Reding <treding at nvidia.com>
> > 
> > Enabling a PLL while IDDQ is high. The Linux kernel checks for this condition and
> > warns about it verbosely, so while this seems to work fine, fix it up according to
> > the programming guidelines provided in the Tegra K1 TRM (v02p), Section
> > 5.3.8.1 ("PLLC and PLLC4 Startup Sequence"). The Tegra114 TRM doesn't
> > contain this information, but the programming of PLLC is the same on Tegra114
> > and Tegra124.
> Do we need this for T210, too? A quick glance at the TRM shows IDDQ for PLLA, M, C, U, P, D.

I suspect that we might need this for Tegra210 as well, though I haven't
encountered the warning yet. That said, I think this is a fairly new
warning, though the code's been in the kernel since essentially forever,
so it could be that I just haven't encountered it on Tegra210 because I
haven't tested with the right U-Boot/kernel combination.

On that note, any ideas on what could've triggered this? I know there
were a couple of changes to the Tegra clock code in U-Boot recently, but
I don't remember seeing anything suspicious.

Thierry

> > Signed-off-by: Thierry Reding <treding at nvidia.com>
> > ---
> >  arch/arm/include/asm/arch-tegra114/clock.h | 3 +++
> >  arch/arm/mach-tegra/tegra114/clock.c       | 5 +++++
> >  2 files changed, 8 insertions(+)
> > 
> > diff --git a/arch/arm/include/asm/arch-tegra114/clock.h
> > b/arch/arm/include/asm/arch-tegra114/clock.h
> > index abbefcd0e456..9bee39778747 100644
> > --- a/arch/arm/include/asm/arch-tegra114/clock.h
> > +++ b/arch/arm/include/asm/arch-tegra114/clock.h
> > @@ -25,4 +25,7 @@
> >  #define OSC_FREQ_SHIFT          28
> >  #define OSC_FREQ_MASK           (0xF << OSC_FREQ_SHIFT)
> > 
> > +/* CLK_RST_CONTROLLER_PLLC_MISC_0 */
> > +#define PLLC_IDDQ		(1 << 26)
> > +
> >  #endif	/* _TEGRA114_CLOCK_H_ */
> > diff --git a/arch/arm/mach-tegra/tegra114/clock.c b/arch/arm/mach-
> > tegra/tegra114/clock.c
> > index cec843b27df7..e6ef873c8dc4 100644
> > --- a/arch/arm/mach-tegra/tegra114/clock.c
> > +++ b/arch/arm/mach-tegra/tegra114/clock.c
> > @@ -629,6 +629,11 @@ void clock_early_init(void)
> > 
> >  	tegra30_set_up_pllp();
> > 
> > +	/* clear IDDQ before accessing any other PLLC registers */
> > +	pllinfo = &tegra_pll_info_table[CLOCK_ID_CGENERAL];
> > +	clrbits_le32(&clkrst->crc_pll[CLOCK_ID_CGENERAL].pll_misc,
> > PLLC_IDDQ);
> > +	udelay(2);
> > +
> >  	/*
> >  	 * PLLC output frequency set to 600Mhz
> >  	 * PLLD output frequency set to 925Mhz
> > --
> > 2.5.0
> 
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