RE: I3C Mastership RFC

[Vitor Soares <Vitor.Soares@synopsys.com>]

Hi Boris,

From: Boris Brezillon <boris.brezillon@collabora.com>
Date: Mon, Nov 25, 2019 at 11:34:52

> On Mon, 25 Nov 2019 11:19:44 +0000
> Vitor Soares <Vitor.Soares@synopsys.com> wrote:
> 
> > > > > > 
> > > > > > I based in all version and tried to pass everything to master.c file.  
> > > > > 
> > > > > I'm not sure what that means, but okay.
> > > > >   
> > > > > > Right now my challenge it to trigger mastership request when a device 
> > > > > > driver want to access to the bus but I believe we can discuss that after.  
> > > > > 
> > > > > That's kind of a basic feature when talking about mastership handover,
> > > > > but sure, we can discuss it after your RFC has been posted.  
> > > > 
> > > > I need to test if the time that device.c request the mastership and the 
> > > > controller has effectively the ownership of the bus is short enough to 
> > > > call i3c_dev_do_priv_xfers_locked(dev->desc, xfers, nxfers) before of all 
> > > > housekeeping of bus takeover.
> > > >   
> > > > > 
> > > > > Note that I'm not super happy to have to go back to square 1 and throw
> > > > > away all of the work done by Przemek, especially since Przemek was the
> > > > > first one to post a patchset and he never really said he didn't
> > > > > want or didn't have time to continue working on this task (not even
> > > > > mentioning the time I spent reviewing those patches...).
> > > > > 
> > > > > If Przemek is fine with this situation I'm okay making an exception,
> > > > > but be aware that it's not how we usually do: the person that posts a
> > > > > patchset first leads the thing (of course, it's even better if there's
> > > > > some kind of coordination before the patch is posted).  
> > > > 
> > > > Honestly it looks like I'm competing on this which is not the case.
> > > > I just pointed out my concerns about this adoption because I see several 
> > > > issues on it. The point is, at the end you can pick some parts of my sec 
> > > > master code and integrate in your solution.
> > > >   
> > > 
> > > Can you point me to the version of the patch your changes are based on?
> > > And also, can you tell me what issues you faced? I would like to check
> > > if they are already adressed in my code.  
> > 
> > I used v3 and v4. From v5, I found useful the switch case (request, 
> > deliver, handoff, takeover) in hc side.
> > 
> > I didn't hardly test how device.c request mastership but I suspect it 
> > won't work properly. When you do i3c_dev_do_priv_xfers_locked() you might 
> > not be the master yet.
> 
> I'm pretty sure we solved that already (that's what
> i3c_master_acquire_bus_ownership() calls are supposed to take care of).
> Can you be a bit more specific? What makes you think the master might
> not be in control of the bus when i3c_dev_do_priv_xfers_locked() is
> called?

You are assuming that after i3c_master_acquire_bus_ownership() return, 
secondary master already owns the bus. Main master can ack the MR request 
and not send the CETACCMST immediately.

I was thinking to delay i3c_dev_do_priv_xfers_locked() with a work delay 
or so. Do you have any idea?

> 
> > 
> > >   
> > > > As I said previous for I3C spec 1.1 secondary master received a big 
> > > > improvement due the misunderstanding published in 1.0 spec. I don't know 
> > > > any other protocol that implement such kind of feature and for this is 
> > > > from far the most complex feature to implement in SO based systems from 
> > > > i3c spec.
> > > >   
> > > > > 
> > > > > BTW, you mentioned working on a lot of different topics, but most of
> > > > > them were left unfinished (userspace i3cdev interface, I3C slave
> > > > > framework/API, ...).  
> > > > 
> > > > The i3cdev does what we discuss during the proposal of i3c subsystem and 
> > > > only expose i3c device without device driver yet I'm not happy with 
> > > > transfer struct.
> > > > For the tools I have for hdr and sdr transfers, for now I didn't feel the 
> > > > need of a tool for ccc (but for testing purposes it would help a lot).
> > > >   
> > > > > Any plans to post RFCs on those aspects anytime
> > > > > soon? I mean, there's plenty of topics to work on, and I'd really prefer
> > > > > that each developer work on a different topic instead of duplicating the
> > > > > effort...
> > > > > 
> > > > > Regards,
> > > > > 
> > > > > Boris  
> > > > 
> > > > Best regards,
> > > > Vitor Soares
> > > > 
> > > >   
> > > 
> > > -- 
> > > -- 
> > > Regards,
> > > Przemyslaw Gaj  
> > 
> > Again sorry for the delay. I will try to send this soon.
> 
> Can you please share what you have now (even if it's not finished) so
> Przemek can start looking at it?

I will try today.

Best regads,
Vitor Soares


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