Re: [virtio-comment] [PATCH v4] virtio-i2c: add the device specification

[Jie Deng <jie.deng@intel.com>]

On 2020/11/12 16:54, Michael S. Tsirkin wrote:
> On Thu, Nov 12, 2020 at 09:51:17AM +0800, Jie Deng wrote:
> > On 2020/11/10 18:59, Paolo Bonzini wrote:
> > > On 10/11/20 11:33, Michael S. Tsirkin wrote:
> > > > > Sorry I didn't reply last week, but I really would prefer if virtio-i2c
> > > > > supported write-read transactions.
> > > > And I think an easier way is to allow multi-segment transactions
> > > > probably using the stop flag.
> > > You cannot always be sure that the host would support them (with the
> > > exception of write+read transactions, which are pretty much universal),
> > > so you would also need to describe what the host features are.
> > >
> > > Paolo
> > Then I will send v5 to support write+read transactions using Paolo's
> > proposal.
> > I think we may have a simple version merged first and then improve it
> > according
> > to the actual needs.
> >
> > Thank you.
> I frankly don't get it, you put read/write flags there even though they
> are not needed, saying it's intended to mirror Linux, then don't want to
> put STOP there even though this is exactly what Linux has ...

Personally, I intended to mirror the Linux "i2c_msg" to have following 
interface.

struct virtio_i2c_req {
ÂÂÂÂÂÂÂ le16 addr;
ÂÂÂÂÂÂÂ le16 flags;
ÂÂÂÂÂÂÂ le16 len;
ÂÂÂÂÂÂÂ u8 buf[];
ÂÂÂÂÂÂÂ u8 status;

};

I intended to implement the standard rules for I2C transactions
(no I2C_FUNC_PROTOCOL_MANGLING) for the first step. So in the
v1~v3 only the "I2C_M_RD" was used and other bits of the flags were 
reserved.
(I2C_M_STOP requires I2C_FUNC_PROTOCOL_MANGLING).

For me, I intend to mirror the "i2c_msg" from the Linux completely.

I learned about Michael also intends to keep above interface but want to
remove some unnecessary bit (e.g. I2C_M_RD) from the flags (Correct me 
if not right).

Paolo prefers following interface without flags.

struct virtio_i2c_req {
	le16 addr;
	le16 written;
	le16 read;
	u8 bufwrite[];
	u8 status;
	u8 bufread[];
};

So Michael and Paolo, I hope we can agree on the interface first.

Any suggestions ?

Thanks.