[Arm-netbook] 2.7.4 preproduction sample, 1.7 MD, Questions
paul at boddie.org.uk
Sun Jul 19 22:32:05 BST 2020
On Sunday, 19 July 2020 22:43:59 CEST Luke Kenneth Casson Leighton wrote:
> On Sun, Jul 19, 2020 at 9:35 PM Paul Boddie <paul at boddie.org.uk> wrote:
> > It looks like the device tree (sun7i-a20-eoma68-a20.dts) is very similar
> > to that from the Cubietruck 2.
> that sounds about right. possibly the original cubieboard.
OK. From what I can see, there are strong similarities between the above file
and both sun4i-a10-cubieboard.dts and sun7i-a20-cubieboard2.dts. (I got mixed
up and wrote Cubietruck 2 above.)
The principal differences appear to be as follows:
The EOMA68-A20 DT doesn't have HDMI nodes whereas the Cubieboard DTs have
nodes for HDMI connectors and the usual peripheral nodes (&hdmi, &hdmi_out).
Given the effort that went into putting micro-HDMI on the computer card, I
guess there might be some definitions to add here.
The EOMA68-A20 DT has a special pinctrl node for mmc3_cd_pin (MMC3 card
detect, I guess). There are also LED pin differences, but I think these are
explained by pin definitions migrating to the sun7i-a20.dtsi file.
Some I2C definitions seem to be different in the Cubieboard DTs, but that
could also be due to pin definitions migrating to the sun7i-a20.dtsi file.
The Cubieboard DTs enable the display engine (&de) and power
There are some changes to the Ethernet node (&gmac). (I didn't think Ethernet
was exposed by the computer cards when the specification was updated after the
first round of cards being made.)
The Cubieboard DTs enable USB OTG (&usb_otg) whereas the EOMA68-A20 DT has a
node ®_usb0_vbus that the other DTs do not have.
So, it seems possible that an updated DT file would be a minor variation on
the Cubieboard 2 file.
> > Were the differences documented and are there any
> > schematics to provide any necessary insight when updating the device tree?
> there's PDFs somewhere... http://hands.com/~lkcl/eoma/
> such as this: http://hands.com/~lkcl/eoma/DS113-V2.7-2017-02-17.pdf
And, as usual, when I go to download it, I find that I already have it
alongside a schematic for the Cubietruck!
> the thing is that it is critically important that the dts file *do
> not* include the peripherals associated with the "Boards"
> (Micro-Desktop, 15in laptop). the peripheral sets *MUST* go into a
> "dynamic include" file that is detected at boot time and "inserted"
> into the live device-tree.
Indeed. I guess the computer card device tree sits at a level between the
chipset device tree and what would normally be the machine device tree.
> this functionality - dynamic runtime "insertion" of device-tree
> fragments - was an idea *in development* back in.... 2013 we have had
> to wait several years for this functionality to make its way into both
> u-boot and the linux kernel.
I guess I should ask whether such support made it into either of them.
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