On 30/09/21 15:04, Daniel Golle wrote:
On Thu, Sep 30, 2021 at 02:49:57PM +0200, Florian Eckert wrote:
Since the update of kernel from 5.4 to 5.10 in the openwrt master branch
[1],
I have problems with additional hardware on the I2C (SMBus) of my APU3.
The Linux upstream removed the platform data support for my I2C IO-Expander
mcp23s08 [3].
Because of this change I could not use my own written platform device
specification anymore.
This is common for this kind of device on x86 which does not support
device-tree.
See for exaple the platform init on the x86 geode board.[5]
If the device supports ACPI, this is now the why to do this [6].
I am still in the process of building the SSDT ACPI table for the i2c
mcp23s08 device connect to the SMBus.
As I now know we could load these SSTD into the kernel during operation or
via an initrd on boot.
you can also load tables from configfs (if you enable that on kernel
compile time).
See the kernel documentation about this feature
https://www.kernel.org/doc/html/latest/admin-guide/acpi/ssdt-overlays.html
As far as I have seen, no initrd is loaded during normal operation [4] on
OpenWrt.
Is there any way to create an initrd to load the ACPI tables and then mount
the initrd so the kernel can load this kind of files?
What would this look like in OpenWrt?
I think it should be just as fine to load them early during boot,
ie. place a script in /lib/preinit/ which does that.
On boards with coreboot like the apu3 the best would probably be to
fix ACPI tables supplied by the BIOS (or swap SeaBIOS for an UEFI
implementation like Tianocore at the same time) instead of patching
things using Linux at runtime.
This isn't a fix, he has added hardware on I2C that is not on standard
on APU3.
Although yes he could compile a custom coreboot with this ACPI table
modification baked in.
-Alberto
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