linux-kernel - RE: [PATCH v7 3/7] i3c: master: add i3c_secondary_master

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Date:   Tue, 12 May 2020 06:42:39 +0000
From:   Parshuram Raju Thombare <pthombar@...ence.com>
To:     Boris Brezillon <boris.brezillon@...labora.com>
CC:     "bbrezillon@...nel.org" <bbrezillon@...nel.org>,
        "vitor.soares@...opsys.com" <vitor.soares@...opsys.com>,
        Przemyslaw Gaj <pgaj@...ence.com>,
        "linux-i3c@...ts.infradead.org" <linux-i3c@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Milind Parab <mparab@...ence.com>,
        "praneeth@...com" <praneeth@...com>
Subject: RE: [PATCH v7 3/7] i3c: master: add i3c_secondary_master_register

>Can you really select the bus mode without knowing the I3C devices you
>have on the bus? Or maybe that's a preliminary initialization which is
>then updated when you receive DEFSLVS events.

I think we can select bus mode based on knowledge of I2C devices on the
bus. I was expecting to support different I2C devices information
on main master and secondary masters. But that seems problematic
for mastership requests. As IMO for mastership acquire and yield to work,
all master capable devices should be operating in same bus mode.

In previous patch set I tried approach of all devices using same (Pure)
bus mode during initialization and updating it on DEFSLVS reception.
But this can cause issue for hot joining devices as current master would
have already switched it's bus mode to something other than pure mode,
and hot join would not work.
To me it's seems for mastership handover to work, we need all masters
to have complete I2C device list on the bus. 

>I suspect you'll have to request bus ownership first, which means
>they're not really usable, just registered to the I2C subsystem. This
>might lead to a whole bunch of problems when drivers will try to send
>messages to the I2C devices and receive ETIMEDOUT/EBUSY errors. We'll
>probably need some updates to the I2C framework if we want I2C to play
>nicely with bus handover, but I think we can keep that for later. I'd
>suggest to forget about I2C for now and mark that as a limitation (no
>I2C devs on secondary masters).

Correct, here I2C devices are just registered. Irrespective of the device type (I2C/I3C)
to which master want to communicate with, bus has to be acquired.

Regards,
Parshuram Thombare