Re: [PATCH] virtio: i2c: Allow buffer less transactions

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

On 2021/7/29 14:28, Viresh Kumar wrote:
> On 29-07-21, 14:18, Jie Deng wrote:
> > The number of descriptors required for a request will not be fixed.
> That is true today as well, as we allow 3 (write or read) or 4
> (write-read) descriptors.
>
> > If there is a descriptor sequence in the virtqueue, then you may need a
> > state machine
> >
> > to parse the sequence. For example, when you have
> >
> >
> > WRÂÂ ÂÂ RR Â ÂÂÂÂ ZR
> >
> > O O IÂÂ O I IÂÂÂÂ O I
> >
> > * WR:(write request), RR (read request), ZR (zero request), O: output
> > descriptor, I: input descriptor
> >
> >
> > When you encounter "O I" combination, you have to read the element after it
> > to distinguish
> >
> > RR and ZR. Will this bring unnecessary difficulties for the backend coding ?
> I understand what you are saying, but at least all the backends that I
> have worked with (Qemu and Rust), further categorizes these into
> blocks and this is how it looks there (writing in qemu terminology):
>
> VuVirtqElement *elem = vu_queue_pop();
>
> elem->in_num and elem_out_num gives the number of out/in buffers
> there.
>
> And so there is no way one can get confused between two different
> elements and you will always know if it is WR or RR or ZR.


Then it's good. Thank you.