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

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Message-ID: <4DBE768F-3CDC-41BE-9CC8-E294E7277CB1@cadence.com>
Date:   Tue, 28 Aug 2018 12:55:20 +0000
From:   Przemyslaw Gaj <pgaj@...ence.com>
To:     Boris Brezillon <boris.brezillon@...tlin.com>,
        vitor <Vitor.Soares@...opsys.com>
CC:     "linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>,
        Sekhar Nori <nsekhar@...com>, Wolfram Sang <wsa@...-dreams.de>,
        "linux-i2c@...r.kernel.org" <linux-i2c@...r.kernel.org>,
        Jonathan Corbet <corbet@....net>,
        "linux-doc@...r.kernel.org" <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" <devicetree@...r.kernel.org>,
        "linux-kernel@...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>,
        Peter Rosin <peda@...ntia.se>
Subject: Re: [PATCH v6 01/10] i3c: Add core I3C infrastructure

Hi Vitor,

I have already implemented Mastership request/handover but we are waiting for Boris’s patch to be accepted and merged. Anyway, my comments below.

On 8/28/18, 2:02 PM, "Boris Brezillon" <boris.brezillon@...tlin.com> wrote:

    EXTERNAL MAIL
    
    
    Hi Vitor,
    
    On Tue, 28 Aug 2018 12:50:12 +0100
    vitor <Vitor.Soares@...opsys.com> wrote:
    
    > 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?

I think we don’t need separate field for secondary master. Main and secondary masters 
support similar functionalities. It’s enough to have this state internally and do mastership it it's needed.

    > 
    > 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 we need to support both.

I agree.
    
    > 
    > 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.
    
    Actually, I was planning on making it completely separate from
    regular slave IBIs. That is, the master controller driver would demux
    the slave, MR and Hot Join IBIs, and if there's an MR request, queue a
    mastership handover work to the workqueue (pretty much what we do for
    Hot-Join already). Mastership handover is anyway likely to be IP
    specific, so I don't think there's a need to make it look like a
    regular IBI.

I think it's better to have separate function to do mastership request.
    
    Regarding whether IBI-MR support should be exposed to the I3C framework
    or not depends on how much will be automated on the framework side. I
    don't the answer yet, but that's probably something will figure out
    along the road.

My current implementation is: when request_mastership field 
of i3c_master_controller_ops structure is set, master driver supports mastership requests.
That's how I check if this is supported or not.
    
    Regards,
    
    Boris
    
Regards,
Przemek