On 29.11.23 20:27, Simon Glass wrote:
> On Wed, 29 Nov 2023 at 12:15, Ahmad Fatoum <a.fatoum@xxxxxxxxxxxxxx> wrote:
>> On 29.11.23 20:02, Simon Glass wrote:
>>> On Wed, 29 Nov 2023 at 11:59, Ahmad Fatoum <a.fatoum@xxxxxxxxxxxxxx> wrote:
>>>> The specification says that this is the root U-Boot compatible,
>>>> which I presume to mean the top-level compatible, which makes sense to me.
>>>>
>>>> The code here though adds all compatible strings from the device tree though,
>>>> is this intended?
>>>
>>> Yes, since it saves needing to read in each DT just to get the
>>> compatible stringlist.
>>
>> The spec reads as if only one string (root) is supposed to be in the list.
>> The script adds all compatibles though. This is not really useful as a bootloader
>> that's compatible with e.g. fsl,imx8mm would just take the first device tree
>> with that SoC, which is most likely to be wrong. It would be better to just
>> specify the top-level compatible, so the bootloader fails instead of taking
>> the first DT it finds.
>
> We do need to have a list, since we have to support different board revs, etc.
Can you give me an example? The way I see it, a bootloader with
compatible "vendor,board" and a FIT with configuration with compatibles:
"vendor,board-rev-a", "vendor,board"
"vendor,board-rev-b", "vendor,board"
would just result in the bootloader booting the first configuration, even if
the device is actually rev-b.
>>>>> + fsw.property_string('description', model)
>>>>> + fsw.property_string('type', 'flat_dt')
>>>>> + fsw.property_string('arch', arch)
>>>>> + fsw.property_string('compression', compress)
>>>>> + fsw.property('compatible', bytes(compat))
>>>>
>>>> I think I've never seen a compatible for a fdt node before.
>>>> What use does this serve?
>>>
>>> It indicates the machine that the DT is for.
>>
>> Who makes use of this information?
>
> U-Boot uses it, I believe. There is an optimisation to use this
> instead of reading the DT itself.
The configuration already has a compatible entry. What extra use is the compatible
entry in the FDT node?
Thanks,
Ahmad
>
> Regards,
> Simon
>
--
Pengutronix e.K. | |
Steuerwalder Str. 21 | http://www.pengutronix.de/ |
31137 Hildesheim, Germany | Phone: +49-5121-206917-0 |
Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-5555 |
