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

[Lokesh Vutla]

On 7/7/2017 8:30 PM, 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.

This identification should eventually use DM + DT. May I know why it
can't use DM I2C in 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

This is right. We should be using the same for SPL as well and
eventually remove non-DM code.

Thanks and regards,
Lokesh

>> 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.
> 
> Jean-Jacques
>>
> 
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