[U-Boot] How do ARM platform initialize DDR?

[Mj Embd]

Hi York,

I was thinking about your problem and this could be a solution
mpc85xx uses a family of ddr controllers.
I believe they would be migrated to LayerScape,

Freescale has also i.mx4/5/6 series and coming i.mx8, that series
uses/might use another ddr controller

Option1
As you suggested which looks a worthy option.
 ddr/fsl/contoller1/ --- for 85xx
 ddr/fsl/contoller2/ --- for I.mx

in your board config file, you might want to use
 CONFIG_DDR_CONTROLLER_MPC85xx
or CONFIG_DDR_CONTROLLER_IMX

PS: I see no direct relation between ddr controller and core, also
freescale is going core agnostic so I think the ddr controller be moved
from cpu folder to driver/ddr folder.

-Regards
mj


On Fri, Sep 20, 2013 at 3:19 AM, York Sun <yorksun at freescale.com> wrote:

> On 09/19/2013 02:33 PM, Tom Rini wrote:
> > On 09/19/2013 05:08 PM, York Sun wrote:
> >> On 09/19/2013 01:57 PM, Tom Rini wrote:
> >>> On Tue, Sep 17, 2013 at 08:59:24AM -0700, York Sun wrote:
> >>>
> >>>> Albert,
> >>>>
> >>>> Pardon me if this is a dumb question. I have been working on
> >>>> powerpc platforms in the past. Now we (the developers I work
> >>>> with) are exploring ARM cores. I am searching how memory is
> >>>> initialized and found different solutions. Some platforms have
> >>>> memory ready before u-boot even starts, some simply write to a
> >>>> set of registers. I understand many platforms don't share the
> >>>> IP of DDR controller. I am wondering if there is generic DDR
> >>>> driver used by many ARM platforms, like the one we have for
> >>>> powerpc/mpc85xx SoCs.
> >>>
> >>> Thinking back, as a rule of thumb, PowerPC has SPD I2C data
> >>> available, usually.  That's not the rule for ARM.  One of a few
> >>> choices happen: 1) ROM sets up DDR. 2) U-Boot/SPL sets up the DDR
> >>> controller.
> >>>
> >
> >> So for ARM platforms, the majority don't have the flexibility of
> >> using different DIMMs and/or clocks?
> >
> > It's a different world.  Again, thinking back to the PowerPC boards
> > I've seen, they had "regular" DDR sockets.  Most ARM boards don't.
> > You can design your board with whatever, and I know in prototyping
> > folks make do swapping chips in and out (and if you look at the omap
> > code, you can see where we have code to calculate the timing values
> > and print them, or use provided hard-coded values).
>
> Understood. We may have boards with DIMM slots. I do see value of a
> fully functional DDR driver here.
>
> >
> >>> The problem is that the DDR controller is usually
> >>> vendor-specific. Perhaps the flip-side here is that there's not
> >>> so much a generic DDR driver for mpc85xx but simply one vendor
> >>> for mpc85xx.  Taking arch/powerpc/cpu/mpc85xx/ddr-gen3.c as what
> >>> you're talking about,
> >>> arch/arm/cpu/armv7/omap-common/emif-common.c would be an
> >>> ARM-world example (the 'EMIF' is found on a large variety of TI
> >>> parts, not just "omap" ones).
> >
> >> Does it make sense to share the Freescale DDR driver across ARM
> >> and Powerpc? Or does it make more sense to selectively copy the
> >> mpc8xxx DDR driver to Freescale ARM subfolder to start with. If the
> >> similarity sustains then we merge them into common driver. If not,
> >> we maintain two separated drivers.
> >
> >> For those who is not familiar with, Freescale is extending products
> >> to ARM cores. I am expecting peripherals stay relatively close, so
> >> many driver can be reused.
> >
> > I've been wondering when this would start to be visible.  If we are
> > able to share the DDR controller code between mpc85xx and the ARM
> > stuff you're talking about, we'll have to sort out someplace within
> > drivers/ to place it, to avoid #include nightmares I suspect.  Other
> > drivers should be easier to share at least :)
> >
>
> I did a quick and dirty hack yesterday to move DDR driver to
> drivers/ddr/fsl. I had to change many #include <asm/????>.
>
> York
>
>
>
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-- 
-mj