linux-kernel - RE: [PATCH v10 7/7] i3c: master: mastership handover, defslvs processing in cdns controller driver

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Date:   Thu, 17 Jun 2021 10:28:11 +0000
From:   Parshuram Raju Thombare <pthombar@...ence.com>
To:     Alexandre Belloni <alexandre.belloni@...tlin.com>
CC:     "slongerbeam@...il.com" <slongerbeam@...il.com>,
        "vitor.soares@...opsys.com" <vitor.soares@...opsys.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 v10 7/7] i3c: master: mastership handover, defslvs
 processing in cdns controller driver

>I don't really get why being a secondary master would be hardcoded in
>the IP. What happens if multiple cadence masters have
>CONF_STATUS0_SEC_MASTER unset and are on the same bus?
>
>Also, it feels weird to let that kind of decision to the master driver.
>I would really think the use case would be that each master on the bus
>is running on a different system. I don't really see the point of having
>the primary and the secondary on the bus on the same system.
>
>Then, we definitively want to let the decision of which master is the
>current master at boot to the HW designer which will depend on what is
>present on the board

Since I3C bus can have only one master at a time, it is necessary to be decide
Which master device is capable of doing initialization which includes assigning
dynamic addresses to all devices and sending DEFLVS, and can be considered
as main master to call i3c_primary_master_register. This decision about which 
master is capable of acting as main master seems controller specific.

Cadence's Master controller IP can act as main master or secondary master.
There are differences in their functionalities. However, if other controllers
support both modes equally, their driver can chose any master device to act
as main master, or use any other controller specific methods to decide main
master. 

>> +	if (secondary)
>> +		INIT_WORK(&master->defslvs_work, cdns_i3c_sec_master_defslvs);
>> +
>Don't you need any master to be able to handle defslvs to be able to
>request mastership?

This is for secondary master only. DEFSLVS is sent by current master, after
DAA, to ensure that all masters have information about all devices on the bus.