Re: I3C Mastership RFC

From: Boris Brezillon <boris.brezillon@collabora.com>
To: Vitor Soares <Vitor.Soares@synopsys.com>
Cc: Przemyslaw Gaj <pgaj@cadence.com>,
	"linux-i3c@lists.infradead.org" <linux-i3c@lists.infradead.org>,
	"bbrezillon@kernel.org" <bbrezillon@kernel.org>
Subject: Re: I3C Mastership RFC
Date: Mon, 25 Nov 2019 14:09:36 +0100	[thread overview]
Message-ID: <20191125140936.47f3d479@collabora.com> (raw)
In-Reply-To: <CH2PR12MB421644B0CAB1DEF50675995EAE4A0@CH2PR12MB4216.namprd12.prod.outlook.com>

On Mon, 25 Nov 2019 13:00:17 +0000
Vitor Soares <Vitor.Soares@synopsys.com> wrote:

> > > > > > 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.
> > > > >    
> > > > 
> > > > In Cadence HC driver, I'm waiting for GETACCMST longer, polling the
> > > > status and after I exit from ->request_mastership(), I'm the bus owner.
> > > > If not, error exit code is returned and we can't make the transfers.
> > > > Are you able to implement the same behavior?    
> > > 
> > > You can assume everyone will do in that way. What happen if you receive a 
> > > request or an information from current master?  
> > 
> > We have this ->request_mastership() method so controllers that have
> > this logic (MR+wait(GETACCMST) automated can still interface with the
> > subsystem.   
> 
> I can also poll the GETACCMST but we are assuming nothing will happen 
> between MR and GETACCMST.

Nothing coming from the master that tries to acquire the bus, yes.
Nothing coming from the current master, no, and that shouldn't be a
problem as long as those operations don't involve acquiring bus->lock.
And if some of those operation involve acquiring the lock (I'd still
need to understand which operation that would be) they'll just be
delayed/rejected.

> 
> > If your controller handles the MR/GETACCMST separately, it
> > shouldn't be hard to implement, and we can even provide an helper if
> > people end up duplicating the code.  
> 
> I already implement a callback in my code so each controller be able to 
> do their stuff in that in request/deliver mastership.

Can you share some details here? What would those callbacks supposed to
do and when would they be called?

_______________________________________________
linux-i3c mailing list
linux-i3c@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-i3c