Re: Does GRUB2 support i2c/smbus communication?

[Frantisek Rysanek]

On 19 Jul 2022 at 17:02, Andrei Borzenkov wrote:
> On 19.07.2022 13:59, Santhosh Nambiar wrote:
> > Hi Community,
> > I would like to know whether GRUB2 supports i2c/smbus communication or not.
> > I have a requirement in which an i2c device has to be accessed from GRUB in
> > an X86 based platform.
> > Appreciate any help you can provide.
> > Thank you.
> 
> There is no generic support. There is some code to access SMBus in
> CS5536 driver, but I guess that's all.
> 
Ahh, the Geode. Still alive and kicking, kind of :-)

The trouble with i2c/smbus is, that the hardware bus interfaces are 
varied, on embedded platforms often outright custom (via GPIO) and 
the bus is not so popular among end users - all of that compared to 
e.g. the USB.
Take Linux for example - the hacker OS platform of choice. 
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tre
e/drivers/i2c
Support for various i2c interfaces is pretty comprehensive: both for 
bus interfaces implemented in silicon (in various popular SoC's / PC 
chipsets / interface converters / NIC's / VGA chips / whatever ), and 
there is some generic API for you to easily implement a driver for 
custom bit-banging interfaces using GPIO (which in itself is a 
diverse family of hardware with no real standard).
Now... how real would it be, to port all that into a bootloader.

I'm afraid that in Grub, you're on your own.

Actually there is one other project that may be closer to Grub than 
Linux, and certainly involves i2c: 
you may want to check out Coreboot.
https://review.coreboot.org/plugins/gitiles/coreboot/+/refs/heads/mast
er/src/drivers/i2c/

Linux or Coreboot, the codebase related to i2c appears to strive for 
a layered approach (for extensibility) and may seem overwhelming to a 
novice :-)

Frank