Fwd: Re: Howto implement bootchooser <-> rauc interaction

[Ahmad Fatoum]

Hi,

On 16.12.21 20:42, Konstantin Kletschke wrote:
> I forgot to address the ML.
> On 2021-12-15 11:50, Ahmad Fatoum wrote:
> 
>> Ye, DT here looks just like arch/arm/dts/imx6qdl-phytec-state.dtsi
> 
> I think you are 100% right. It is borrowed from
> https://bootlin.com/blog/another-system-update-adventure-with-rauc-barebox-yocto-project/
> and I thing this exact file is displayed as an example there.
> 
>> This is fixed in Linux upstream since 0445efacec75 ("nvmem: core: skip child nodes not
>> matching binding"), first included with v5.12-rc1. This has been backported to older
> 
> Okay, this information is extremely useful. I have seen your intital patch series but was
> not able yet to gather information what commit in what time relates to roughly what
> kernel version. So I am involved because I have 5.10.1n here. I will check to update
> to a newer one but do you have a backport for this available by chance for 5.10.1x?

It was backported to stable in v5.10.20. Backport commit is 663a18271.

>> The parent node has #address-cells and #size-cells, which describe how much 32-bit
>> cells are offset and length. For #address-cells = 1 and #size-cells = 1, X is offset
>> and Y is length.
> 
> So one has to take care of the parent note size being big enough to contain the sum of
> all length and thse itself must not overlap, right?

Yes. Device Tree compiler helps here a bit by warning if two nodes on the same bus
have the same base address.

>>> What me bugs more is, how should a devicetree setup look like (is there a reasonable example?)
>>> to make the same in a file in the first FAT partition, is this possible? In the state specification
>>> I read it should be able to be done by a file but ... I don't get it.
>>
>> I can't follow. What do you want to place in the FAT partition? The state itself?
>> The DT describing it? What bothers you about the current setup? (DT description
>> and state in EEPROM).
> 
> I am sorry I did create confusion.
> I did a mistake somehow. When I have the EEPROM setup up and running (may be tomorrow? Always other
> work looks more important) this was only for me to understand barebox-state fully to
> work with this for production use later upon.
> 
> Because the mistake is, I _totally_ forgot when in production the Beaglebone Black I2C EEPROM
> is write protected. The EEPROM's WP pin is hard pulled up on those boards with no chance
> other than solder a wire to the pin to ground (against the pullup resistor). I forgot,
> my daily work golden example has a wire but we sell so much that I must avoid using
> the EEPROM because I cant solder wires onto every BBB.
> 
> I need to put the state somewhere else, into the MBR, before partition table (1st partition?)
> or I need to find some NVRAM elsewhere on the board (PHY, CPU...).
> 
>> You can place state in EEPROM. It looks very similar to your snippet above,
>> but your backend partition will be a MMC OF partition.
> 
>> That's indeed a bit rough around the edges. You can keep unpartitioned space at the start
>> of the MMC device and partition it with OF and have regular MBR/GPT partition start at
>> a later offset. barebox will warn you if they overlap.
> 
> So state in MMC will be an OF partition which must or be covered or overlap with MBR
> partitioning, right? What does the "OF" mean?

Open Firmware. It's the original standard that described device trees.

> On the other hand I am shure in MBR the 1st 446 bytes are available because the TI am335x
> CPU is ignoring it while searching for a bootable flagged FAT and loads BL from there...
> On the other hand, I could access plenty of space unallocated after the MBR if 1st partition
> starts at a late sector like 1024 or so.

Latter is what I usually do.

> And what I understood from the examples, documentation is how to access exactly what byte
> in an EEPROM, but how do I setup and access the bytes at 0x100 to 0x300 in the MMC at
> mmc1 interface or the bytes 0x1000 to 0x2000?

arch/arm/dts/imx6qdl-prti6q-emmc.dtsi places it on eMMC. Check it out.

> And is doing this state thing in a file (for example on the 1st  FAT where barebox.env is)
> for barebox and raux/barebox-state possible or not?

FAT isn't power-fail safe. It's ok for reading or writing stuff during
development (e.g. environment), but you really don't want to use it
for barebox-state that's meant to be power-fail safe.

You can of course use a MBR partition, but raw, without a file system.

>> For devices with an EEPROM, I'd use EEPROM for state over everything else.
> 
> You are right, I will search for some place rather than the file or MMC thingy because
> i chose it because it looks most convenient, but as said, Write Only in produktion.
> 
>> If your only issue is the kernel error above, just import the patch
>> (or update to a newer more shiny Linux release :-)
> 
> No, no problem with either updating the kernel or patching it, the latter is at the project's
> state actually more convenient I - admit.
> 
> HTH.
> 
> Very much, thanks for your friendly elaboration :-)
> 
> Regards
> Konstantin
> 
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