linux-kernel - Re: [PATCH v6 01/10] i3c: Add core I3C infrastructure

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Date:   Tue, 28 Aug 2018 12:50:12 +0100
From:   vitor <Vitor.Soares@...opsys.com>
To:     Boris Brezillon <boris.brezillon@...tlin.com>,
        vitor <Vitor.Soares@...opsys.com>
CC:     <linux-gpio@...r.kernel.org>, Sekhar Nori <nsekhar@...com>,
        Wolfram Sang <wsa@...-dreams.de>, <linux-i2c@...r.kernel.org>,
        Jonathan Corbet <corbet@....net>, <linux-doc@...r.kernel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Arnd Bergmann <arnd@...db.de>,
        Przemyslaw Sroka <psroka@...ence.com>,
        Arkadiusz Golec <agolec@...ence.com>,
        Alan Douglas <adouglas@...ence.com>,
        Bartosz Folta <bfolta@...ence.com>,
        Damian Kos <dkos@...ence.com>,
        Alicja Jurasik-Urbaniak <alicja@...ence.com>,
        "Cyprian Wronka" <cwronka@...ence.com>,
        Suresh Punnoose <sureshp@...ence.com>,
        "Rafal Ciepiela" <rafalc@...ence.com>,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
        Nishanth Menon <nm@...com>, Rob Herring <robh+dt@...nel.org>,
        Pawel Moll <pawel.moll@....com>,
        Mark Rutland <mark.rutland@....com>,
        Ian Campbell <ijc+devicetree@...lion.org.uk>,
        "Kumar Gala" <galak@...eaurora.org>, <devicetree@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        Xiang Lin <Xiang.Lin@...aptics.com>,
        Przemyslaw Gaj <pgaj@...ence.com>,
        Peter Rosin <peda@...ntia.se>
Subject: Re: [PATCH v6 01/10] i3c: Add core I3C infrastructure

Hi Boris,

The DT Bindings say "The node describing an I3C bus should be named 
i3c-master.". Do you have a field for secondary master?

On 24-08-2018 19:16, Boris Brezillon wrote:
> Well, before even considering supporting secondary master registration,
> we need to handle mastership handover. As for the DAA operation, it's
> likely to be host specific, so we'll have to add a new hook to the
> i3c_master_controller_ops struct.
Do you mean when master try to delegate the bus ownership through 
GETACCMST? or to get the bus ownership with IBI-MR?

I think that could be useful to pass the ibi type on request_ibi(), 
there is some case where the master doesn't support IBI-MR.

> Once you've done that, we'll have trigger a mastership handover
> everytime an I3C driver tries to send a frame on the bus, and the
> master this frame should do through is not in control of the bus. That
> should be pretty easy for the nominal case, but error cases are likely
> to be hard to deal with.
> Note that I have a ->cur_master field in the i3c_bus object which
> stores allows us to track whose the currently active master. If
> master->this != master->bus->cur_master that means you need to start a
> mastership handover procedure.
>
> That's all I thought about for now, and we'll probably face other
> problems when implementing it. Let me know if you have other questions,
> and don't hesitate to share your code early during the development
> phase.
>
> Also note that the bus representation is likely to change based on
> Arnd's feedback, so you might have to rework your implementation a bit
> at some point.
>
> Regards,
>
> Boris

Best regards,
Vitor Soares