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

From: Michael Walle <mwalle@kernel.org>
To: Simon Glass <sjg@chromium.org>
Cc: miquel.raynal@bootlin.com, conor+dt@kernel.org,
	devicetree@vger.kernel.org, krzysztof.kozlowski+dt@linaro.org,
	linux-kernel@vger.kernel.org, linux-mtd@lists.infradead.org,
	ptyadav@amazon.de, rafal@milecki.pl, richard@nod.at,
	robh+dt@kernel.org, robh@kernel.org, trini@konsulko.com,
	u-boot@lists.denx.de, vigneshr@ti.com
Subject: Re: [PATCH v2 1/3] dt-bindings: mtd: fixed-partitions: Add binman compatible
Date: Fri, 06 Oct 2023 10:37:41 +0200	[thread overview]
Message-ID: <27d37d4c7cf353d99737a1e7a450f9f7@kernel.org> (raw)
In-Reply-To: <CAPnjgZ2PnKD5m0EgTdEAf-gcK3wuBZvWw_AO2iehb1dmfdoz3A@mail.gmail.com>

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

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