Hi Jeremy

From: Jeremy Kerr <jk@codeconstruct.com.au>
Sent: Friday, August 27, 2021 12:37 PM

Hi Chiawei,

quoted

The eSPI slave device comprises four channels, where each of them has
individual functionality.  Putting the four channels driver code into
a single file makes it hard to maintain and trace.

Yep, understood.

quoted

We did consider to make them standard .c files.
But it requires to export channel functions into kernel space although
they are dedicated only to this eSPI driver.

What do you mean by "export into kernel space" here? The function prototypes

The channel functions will be visible to all kernel driver files.

need to be available to your main (-ctrl.c) file, regardless of whether you're
putting the entire functions in a header file, or just the prototype. There's
doesn't need to be any difference in visibility outside of your own module if
you were to do this the usual way.

Maybe I was trying to make channels function visible only to espi-ctrl.c too far.
I will revise the driver to present in the usual .c way.

quoted

As espi-ctrl needs to invoke corresponding channel functions when it
is interrupted by eSPI events.

To avoid polluting kernel space, we decided to put driver code in
header files and make the channel functions 'static'.

BTW, I once encountered .c file inclusion in other projects. Is it
proper for Linux driver development?

It can be, just that in this case it's a bit unusual, and I can't see a good reason
for doing so. This could just be a standard multiple-source-file module.

quoted

eSPI communication is based on the its cycle packet format.
We intended to let userspace decided how to interpret and compose
TX/RX packets including header, tag, length (encoded), and data.
IOCTL comes to our first mind as it also works in the 'packet' like
paradigm.

But you're not always exposing a packet-like interface for this. For example,
your virtual-wire interface just has a get/set interface for bits in a register
(plus some PCH event handling, which may not be applicable to all
platforms...).

The other channels do look like more of a packet interface though, but in that
case I'm not convinced that an ioctl interface is the best way to go for that.
You're essentially sending a (length, pointer) pair over the ioctls there, which
sounds more like a write() than an ioctl().

In most cases, yes. 
Currently only the peripheral channel has more than the 2 (put tx/get rx) IOCTL code.
We think it might be a good idea to make the user interfaces of all channels consistent using IOCTL.

Regardless of the choice of interface though, this will definitely need some
documentation or description of the API, and the ioc header to be somewhere
useful for userspace to consume.

With that documented, we'd have a better idea of how the new ABI is
supposed to work.

Sure. more comments will be added in aspeed-espi-ioc.h to describe the usage and the purpose.

Thanks for your feedback.

Chiawei