[U-Boot] [PATCH] sunxi: Fix sun5i mbus speed when booting old kernels

[Siarhei Siamashka]

On Fri, 20 Feb 2015 09:44:44 +0100
Hans de Goede <hdegoede at redhat.com> wrote:

> Hi,
> 
> On 20-02-15 09:15, Siarhei Siamashka wrote:
> > On Thu, 19 Feb 2015 14:59:16 +0100
> > Hans de Goede <hdegoede at redhat.com> wrote:
> >
> >> Older linux-sunxi-3.4 kernels override our PLL6 setting with 300 MHz,
> >> halving the mbus frequency, so set it to 300 MHz ourselves and base the
> >> mbus divider on that.
> >>
> >> Signed-off-by: Hans de Goede <hdegoede at redhat.com>
> >> ---
> >>   arch/arm/include/asm/arch-sunxi/clock_sun4i.h | 9 +++++++++
> >>   1 file changed, 9 insertions(+)
> >>
> >> diff --git a/arch/arm/include/asm/arch-sunxi/clock_sun4i.h b/arch/arm/include/asm/arch-sunxi/clock_sun4i.h
> >> index d297ed0..c28ee05 100644
> >> --- a/arch/arm/include/asm/arch-sunxi/clock_sun4i.h
> >> +++ b/arch/arm/include/asm/arch-sunxi/clock_sun4i.h
> >> @@ -144,7 +144,16 @@ struct sunxi_ccm_reg {
> >>
> >>   #define PLL1_CFG_DEFAULT	0xa1005000
> >>
> >> +#if defined CONFIG_OLD_SUNXI_KERNEL_COMPAT && defined CONFIG_MACH_SUN5I
> >> +/*
> >> + * Older linux-sunxi-3.4 kernels override our PLL6 setting with 300 MHz,
> >> + * halving the mbus frequency, so set it to 300 MHz ourselves and base the
> >> + * mbus divider on that.
> >> + */
> >> +#define PLL6_CFG_DEFAULT	0xa1009900
> >> +#else
> >>   #define PLL6_CFG_DEFAULT	0xa1009911
> >> +#endif
> >>
> >>   /* nand clock */
> >>   #define NAND_CLK_SRC_OSC24		0
> >
> > Are there any good reasons to use 600MHz instead of 300MHz for PLL6 in
> > the default u-boot build?
> >
> > Maybe PLL6 can be just set to 300MHz for sun5i in all cases, regardless
> > of the CONFIG_OLD_SUNXI_KERNEL_COMPAT define?
> 
> Basically the reasons are the same as why you want to keep PLL5 running
> at a high speed, PLL6 is a potential parent PLL for all mod0 clk using
> peripherals, and having it higher gives us more possible clocks.

Sure, I just expected a more concrete example out of curiosity.

PLL5P is a bit special, because it is tied to the DRAM clock frequency
and may vary on different boards (because different boards use different
DRAM clock speeds). But there is less variation possible for PLL6.

> I agree that this (and the PLL5 speed) are an issue we need a better fix
> for then CONFIG_OLD_SUNXI_KERNEL_COMPAT if at all possible.
> 
> I'll discuss this further as a reply to your:
> "[PATCH] sunxi: Machine id hack to prevent loading buggy sunxi-3.4 kernels"
> mail.

Thanks.

-- 
Best regards,
Siarhei Siamashka