[U-Boot] [PATCH] spl: dm: Make it possible for the SPL to pick its own DTB from a FIT

[Tom Rini]

On Fri, Jul 07, 2017 at 05:00:50PM +0200, Jean-Jacques Hiblot wrote:
> 
> 
> On 07/07/2017 16:30, Tom Rini wrote:
> >On Fri, Jul 07, 2017 at 01:44:39PM +0200, Jean-Jacques Hiblot wrote:
> >
> >>u-boot can be embedded within a FIT image with multiple DTBs. It then
> >>selects at run-time  which one is best suited for the platform.
> >>Use the same principle here for the SPL: put the DTBs in a FIT image,
> >>compress it (LZO, GZIP, or no compression) and append it at the end of the
> >>SPL.
> >>
> >>Signed-off-by: Jean-Jacques Hiblot <jjhiblot at ti.com>
> >>---
> >>
> >>The impact in terms of boot time is not high when using LZO but I gues it can vary
> >>from platform to platform.
> >>The size of the SPL binary is increased (1.5kB more code on ARM), but the compression
> >>really flattens the DTBS. so at the end of the day, enabling this option doesn't add much.
> >>
> >>Here are some sumbers with a DRA7 platform (numbers in bytes):
> >>                           size  delta with ref
> >>   MLO.reference         123450
> >>   MLO.lzo_1_DTB         123715    +265
> >>   MLO.lzo_4_DTB         124237    +787
> >>   MLO.gzip_4_DTB        132006    +8556
> >>   MLO.no_comp_4_DTB     134184    +10734
> >Bearing in mind that you said in a follow up this is RFC, I'm ignoring
> >all of the stuff that I believe you would fix in a v1.  At the heart of
> >it, are you able to tell different boards before you have a DTB loaded?
> In my case (DRA7) the board can be identified before the dtb is
> loaded. The identification
> is done by reading an eeprom on I2c. It just can't be using DM I2C
> in the SPL.
> >I keep coming back to the problem that for SPL it seems like we should
> >be able to do what Franklin did for keystone
> >(https://patchwork.ozlabs.org/patch/777242/) and have a 'fake' dts file
> >that represents the SoC such that any real boards can get U-Boot loaded
> >and from there have the real board dtb be used.  Or am I forgetting
> >something?  Thanks!
> That's more or less the situation now with DRA7. This idea comes
> from the need to accelerate the fastboot path by using the HS200
> mode of the eMMC. There we need to configure the lines of the eMMC
> and this information is typically found in the DTB and differs from
> SOC to SOC. At the moment in the ti tree this is done by duplicating
> this information in C structures protected with #ifdef
> CONFIG_SPL_BUILD. While this works, it would be nicer to get it from
> the dtb as done in u-boot.

OK.  Lets move forward with seeing what this looks like as a clean
series of patches with everything new being opt-in, thanks!

-- 
Tom
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