[U-Boot] [linux-sunxi] [UBOOT] Both Linux-Sunxi and Mainline Uboot have issues

[Siarhei Siamashka]

On Thu, 19 Feb 2015 14:57:14 +0100
Hans de Goede <hdegoede at redhat.com> wrote:

> Hi,
> 
> On 19-02-15 13:38, Siarhei Siamashka wrote:
> > On Wed, 18 Feb 2015 22:29:07 -0800 (PST)
> > TsvetanUsunov <tsvetanusunov at gmail.com> wrote:
> >
> >> Hi
> >>
> >> For A13-OLinuxino till now we conservatively used the Linux-Sunxi uboot,
> >> but we recently got new lot of Samsung memories and we decided to tweak
> >> some parameters for this DDR in Linux-Sunxi uboot and found problems.
> >> As this uboot is with status not maintained anymore I will not discuss the
> >> problems, as probably no one will spend time on it,
> 
> <snip>
> 
> >> The PLL5 and PLL6 values are changed and this cause problems, this is what
> >> we found so far:
> 
> <snip>
> 
> >> 1. mainline u-boot
> >> =================
> >> 1.1 pll5
> >> address 0x01c20020, value 0xb1049091 - P=1, N=16, K=2, M=2.
> >>   The PLL5 output for DDR = (24MHz*N*K)/M. DDR=24*16*2/2 = 384MHz
> >> The PLL5 output for other module = (24MHz*N*K)/P. DDR=24*16*2/1 = 768MHz  -
> >> This high frequency cause LCDs connected to the board to flicker
> >
> > Yes, this was already known. And had been addressed a long time ago.
> > Hans has a more detailed reply, so I'm not going to duplicate it.
> >
> >> 1.2 pll6
> >> address 0x01c20028, value 0xA1009900 - N=25, K=1, M=1
> 
> This is not the value set by u-boot, u-boot sets this to
> 0xA1009911
> 
> >>   The PLL6 output is (24MHz*N*K)/M/2 = 24*25*1/1/2 = 300MHz
> 
> And this formula from the A13 user manual is wrong I've run several
> tests and the formula from the A10/A20 user manual, as used by the
> allwinner kernel sources, upstream u-boot and upstream kernel:
> 
> PLL6 = (24MHz*N*K)/2
> 
> Is the correct one. This means that what u-boot is doing:
> 
> PLL6 = 0xA1009911, MBUS = 0x81000001
> 
> Results in PLL6 = 600 MHz , MBUS = 600 / 2 = 300 MHz so upstream
> u-boot actually gives you more MBUS bandwidth to work with, as
> intended.
> 
> But then the linux-sunxi-3.4 kernel comes along and sets PLL6 to:
> 0xA1009900 which translates to 300 MHz (in both the wrong and
> correct formula) and you end up with an MBUS of only 150 MHz.
> 
> 
> 
> >> 1.3 MBUS clock
> >> address 0x01c2015c, value 0x81000001  - MBUS clock source is PLL6/2 = 300/2
> >> = 150MHz - This is connected to PLL6 setup, at this 150 Mhz the board cant
> >> play video smoothly and sometimes drop video packets when the video is
> >> playing
> >
> > Right. Having a reasonably fast MBUS clock speed is very important for
> > performance.
> >
> >>   2. sunxi u-boot
> >> =================
> >> 1.1 pll5
> >> address 0x01c20020, value 0xb1049091 - P=2, N=17, K=2, M=2.
> >>   The PLL5 output for DDR = (24MHz*N*K)/M. DDR=24*17*2/2 = 408MHz
> >> The PLL5 output for other module = (24MHz*N*K)/P. DDR=24*16*2/2 = 408MHz  -
> >> this frequency was OK, There is no problem with LCD flickering, why the
> >> frequency increase was necessary?
> >> 1.2 pll6
> >> address 0x01c20028, value 0xA1009900 - N=25, K=1, M=1
> >>   The PLL6 output is (24MHz*N*K)/M/2 = 24*25*1/1/2 = 300MHz
> >
> > Thanks a lot for finding and reporting this particular problem.
> >
> > Based on a quick look, the most likely culprit seems to be the
> > 'c' function in u-boot, which is providing wrong
> > information to the DRAM code. But Hans is already working on a
> > fix, so I'm not going to get involved yet.
> 
> Nope, the user manual for A13 is wrong (see above).

You are right, thanks.

I felt that something was odd, because I did run some memory benchmarks
on an A13-OLinuXino-Micro board earlier (with the mainline kernel) an
did not notice any PLL6 related anomalies at that time:

    http://linux-sunxi.org/A10_DRAM_Controller_Performance

The "300 MHz MBUS" results (MBUS is clocked from PLL6) are more or less
consistent with the others (when MBUS is clocked from PLL5P).

> > Additionally, the sunxi-3.4 kernel is trying to re-configure PLL6 in
> > 'arch/arm/mach-sun5i/clock/clock.c', which is a bit of a mess. As you
> > have the problem, most likely it also ends up being 300MHz there.
> > Probably the sunxi-3.4 kernel should not touch PLL6 at all and keep
> > the settings from u-boot.
> 
> Oh, thanks for pointing that out, that explains why Tsvetan is seeing
> 0xA1009900 for the PLL6 setting, and explains his problem (see analysis
> above).
> 
> I've attached a patch which should fix this, Tsvetan note that you
> need to build with old kernel compatibility enabled for this fix to
> work, as explained in my previous mail. Please let me know if this
> fixes things then I'll push it upstream ASAP.
> 
> And someone should also write a kernel patch for the linux-sunxi kernel
> to not touch pll6 on sun5i.

I have looked at it a bit. And now I don't feel like touching anything
PLL6 related in the sunxi-3.4 kernel. The A20 and A13 manuals contain
some rather confusing information about PLL6 (all these PLL6, PLL6*2,
PLL6/2, the M divisor, etc.). The sunxi-3.4 kernel sources are rather
convoluted too.

So I'm not quite sure whether changing PLL6 from 300MHz to 600MHz (by
keeping the default PLL6 settings from u-boot) in the sun5i build of the
sunxi-3.4 kernel is really free from any regressions. We might upset
Tsvetan again :)

-- 
Best regards,
Siarhei Siamashka