[U-Boot] [PATCH] mx6: Add initial SPL support for HummingBoard-i2eX

[Fabio Estevam]

Hi Nikolay,

On Wed, Apr 15, 2015 at 8:18 PM, Nikolay Dimitrov <picmaster at mail.bg> wrote:

> This mem_speed (1600) means that the MMDC imx6 code will calculate
> timings for 1600 MT/s, but in reality the memory clock will be 528 or
> 532 MHz. It would be better to override the speed to 1066 to make
> sure imx6 ddr code calculates proper timings.

mem_speed should be retrieved from the DDR3 datasheet.

For clarification, take a look at: board/gateworks/gw_ventana/gw_ventana_spl.c

/* MT41K128M16JT-125 */
static struct mx6_ddr3_cfg mt41k128m16jt_125 = {
    .mem_speed = 1600,

Looking at the MT41K128M16JT-125 datasheet it says it has a cycle time
of 1.25ns, which corresponds
to 800MHz. Since this is DDR (double rate) then you get 1600MHz.

> To be honest, I don't understand why the code (arch/arm/cpu/armv7
> /mx6/ddr.c) supports 1333/1600 MT/s when it's obvious that it's outside
> chip specs.

The chip is not out of spec. In this ddr.c file we have:

    /* MX6D/MX6Q: 1066 MHz memory clock, clkper = 1.894ns = 1894ps */
    if (is_cpu_type(MXC_CPU_MX6Q) || is_cpu_type(MXC_CPU_MX6D)) {
        clock = 528;
        tcwl = 4;
    }

> And a couple of more notes:
> - I see that you don't use the extlinux boot mechanism (from distro
> defaults). Do you see any advantages of not using it?

No, I don't. This could be added later.

> - Would be nice to have HDMI support :)

Yes, HDMI, USB, PCI, SATA etc. One step at time ;-)


> - git patch gives a warning about one empty line

Thanks, I noticed this on the README file and will fix it in v2.

Regards,

Fabio Estevam