Hi Chiawei,

The eSPI on BMC side is a slave device. Most of time it listen to the
Host requests and then react.
This makes it not quite fit to interfaces that act as a master role.

That's a good point, but I don't think it precludes using existing
interfaces.

quoted

1) The VW channel is essentially a GPIO interface, and we have a
kernel ?? subsystem to expose GPIOs. We might want to add additional
support ?? for in-kernel system event handlers, but that's a minor
addition that ?? can be done separately if we don't want that
handled by a gpio ?? consumer in userspace.

eSPI VW channel can be used to forward a byte value to/from GPIO.

I'm not referring to the hardware GPIOs that can be connected here,
rather the logic values represented over the VW channel. The eSPI master
is transferring IO states over the channel, and we could represnt those
on the BMC side as "virtual" GPIOs.

If that model doesn't fit though, that's OK, but I think we need some
rationale there.

quoted

2) The out-of-band (OOB) channel provides a way to issue SMBus
?? transactions, so could well provide an i2c controller interface.
?? Additionally, the eSPI specs imply that this is intended to
support
?? MCTP - in which case, you'll *need* a kernel i2c controller
device to
?? be able to use the new kernel MCTP stack.

Could you share us more information about the i2c need of kernel MCTP
kernel stack?

The currently proposed mctp-i2c interface driver binds to a kernel i2c
device. If you expose a kernel i2c device here, we can connect that as
an MCTP interface.

With the packet interface proposed here, we can't do that, and would
need a whole new driver for this, implemented in userspace. The same
would apply to any other usage of the i2c bus (EEPROM access, etc).

quoted

3) The flash channel exposes read/write/erase operations, which
would be
?? much more useful as an actual flash-type device, perhaps using
the
?? existing mtd interface? Or is there additional functionality
?? expected for this?

The flash channel works in either the Master Attached Flash Sharing
(MAFS) or Slave Attached Flash Sharing (SAFS) mode.

For MAFS, BMC issues eSPI flash R/W/E packets to the Host.
In this case, it may fit into the MTD interface.

For SAFS (mostly used), BMC needs to listen, parse and filter eSPI
flash R/W/E packets from the Host.
And then send replies in the eSPI success/unsuccess completion packet
format.
This behaves differently from MTD.

To support both the two scenario, the MTD interface might not be
suitable.

OK, that makes sense. In this case the BMC is acting as the virtual
flash device, right?

quoted

4) The peripheral channel is the only one that would seem to require
arbitrary cycle access, but we'll still need a proper uapi
definition to support that. At the minimum, your ioctl definitions
should go under include/uapi/ - you shouldn't need to duplicate the
header into each userspace repo, as you've done for the test
examples.

In the first submission, I was told that the include/uapi patch is
not going to be accepted.

This is what you were told in the v1 submission:

quoted

 create mode 100644 include/uapi/linux/aspeed-espi.h

This userspace interface is not going to be accepted upstream.

It sees like that was a comment about the API itself, not the location
of the header (Rob, correct me if I'm wrong). Simply moving the header
out of the uapi directory, while retaining the same API, is not a
solution to this.

In summary, considering the various applications that might be
constructed upon eSPI transaction,
we thought that the raw packet paradigm might be the first step to
start with.

Keep in mind that you're creating a kernel ABI here, which has to stay
in place forever - even if it's the first step to something else, we
cannot break future compatibility.

Regards,


Jeremy