Re: [PATCH v2 1/3] dt-bindings: mtd: fixed-partitions: Add binman compatible

[Michael Walle]

Hi,

> > I'm still not sure why that compatible is needed. Also I'd need to
> > change
> > the label which might break user space apps looking for that specific
> > name.
> >
> > Also, our board might have u-boot/spl or u-boot/spl/bl31/bl32, right 
> > now
> > that's something which depends on an u-boot configuration variable,
> > which
> > then enables or disables binman nodes in the -u-boot.dtsi. So in linux
> > we only have that "bootloader" partition, but there might be either
> > u-boot+spl or u-boot+spl+bl31+bl32.
> >
> > Honestly, I'm really not sure this should go into a device tree.
>
> I think we might be getting a bit ahead of ourselves here. I thought
> that the decision was that the label should indicate the contents.
> If you have multiple things in a partition then it would become a
> 'section' in Binman's terminology. Either the label programmatically
> describes what is inside or it doesn't. We can't have it both ways.
> What do you suggest?

As Rob pointed out earlier, it's just a user-facing string. I'm a bit
reluctant to use it programatically.
Taking my example again, the string "bootloader" is sufficient for a
user. He doesn't care if it's u-boot with spl or u-boot with tfa, or
even coreboot. It just says, "in this partition is the bootloader".
If you have an "bootloader" image you can flash it there.

If it has a label "u-boot" and I want to switch to coreboot, will
it have to change to "coreboot"? I really don't think this is practical,
you are really putting software configuration into the device tree.

> At present it seems you have the image described in two places - one
> is the binman node and the other is the partitions node. I would like
> to unify these.

And I'm not sure that will work for all the corner cases :/

If you keep the binman section seperate from the flash partition
definition you don't have any of these problems, although there is
some redundancy:
 - you only have compatible = "binman", "fixed-partition", no further
   compatibles are required
 - you don't have any conflicts with the current partition descriptions
 - you could even use the labels, because binman is the (only?) user

But of course you need to find a place where to put your node.

> What does user space do with the partition labels?

I'm not sure. Also I'm not sure if it really matters, I just wanted to
point out, that you'll force users to change it.

-michael

> > >> What if a board uses eMMC to store the firmware binaries? Will that
> > >> then
> > >> be a subnode to the eMMC device?
> > >
> > > I thought there was a way to link the partition nodes and the device
> > > using a property, without having the partition info as a subnode of
> > > the device. But I may have imagined it as I cannot find it now. So
> > > yes, it will be a subnode of the eMMC device.
> >
> > Not sure if that will fly.
>
> I can't find it anyway. There is somelike like that in
> simple-framebuffer with the 'display' property.
>
> Regards,
> SImon