Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Date:   Tue, 27 Feb 2018 22:14:07 +0100
From:   Boris Brezillon <boris.brezillon@bootlin.com>
To:     Przemyslaw Sroka <psroka@cadence.com>
Cc:     Vitor Soares <Vitor.Soares@synopsys.com>,
        Boris Brezillon <boris.brezillon@free-electrons.com>,
        Wolfram Sang <wsa@the-dreams.de>,
        "linux-i2c@vger.kernel.org" <linux-i2c@vger.kernel.org>,
        Jonathan Corbet <corbet@lwn.net>,
        "linux-doc@vger.kernel.org" <linux-doc@vger.kernel.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Arnd Bergmann <arnd@arndb.de>,
        Arkadiusz Golec <agolec@cadence.com>,
        Alan Douglas <adouglas@cadence.com>,
        Bartosz Folta <bfolta@cadence.com>,
        Damian Kos <dkos@cadence.com>,
        Alicja Jurasik-Urbaniak <alicja@cadence.com>,
        Cyprian Wronka <cwronka@cadence.com>,
        Suresh Punnoose <sureshp@cadence.com>,
        Thomas Petazzoni <thomas.petazzoni@free-electrons.com>,
        Nishanth Menon <nm@ti.com>, Rob Herring <robh+dt@kernel.org>,
        Pawel Moll <pawel.moll@arm.com>,
        Mark Rutland <mark.rutland@arm.com>,
        Ian Campbell <ijc+devicetree@hellion.org.uk>,
        Kumar Gala <galak@codeaurora.org>,
        "devicetree@vger.kernel.org" <devicetree@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Geert Uytterhoeven <geert@linux-m68k.org>,
        Linus Walleij <linus.walleij@linaro.org>
Subject: Re: [PATCH v2 2/7] i3c: Add core I3C infrastructure
Message-ID: <20180227221407.0cd7f8a9@bbrezillon>
In-Reply-To: <MWHPR07MB278357B74A7D7E31EB109DC5CAC00@MWHPR07MB2783.namprd07.prod.outlook.com>
References: <20171214151610.19153-1-boris.brezillon@free-electrons.com>
        <20171214151610.19153-3-boris.brezillon@free-electrons.com>
        <b39f9016-b2ff-6d8d-96b3-945f32ab2b67@synopsys.com>
        <20180223213000.407461d2@bbrezillon>
        <1b8fe82f-079b-6f55-0e59-5773027faa8e@synopsys.com>
        <20180226213607.7161bb0a@bbrezillon>
        <b9c057ad-47a0-fa35-0f30-8d465d40b6f0@synopsys.com>
        <MWHPR07MB27833F0CAD2597BFDD37CE6CCAC00@MWHPR07MB2783.namprd07.prod.outlook.com>
        <20180227211302.26f76427@bbrezillon>
        <MWHPR07MB278357B74A7D7E31EB109DC5CAC00@MWHPR07MB2783.namprd07.prod.outlook.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=US-ASCII
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Tue, 27 Feb 2018 20:24:43 +0000
Przemyslaw Sroka <psroka@cadence.com> wrote:


> > > SETDASA is simply faster than ENTDAA, but only if there is no
> > > need to collect BCR/DCR/PID of such devices. I think most
> > > applications would like to have them as an status information so
> > > after all ENTDAA can be regarded as an generic approach (unless
> > > I'm mistaken).  
> > 
> > Actually, we could retrieve BCR/DCR/PID (and all other relevant
> > information, like MAXDS) even with the SETDASA approach. We just
> > need to send the according CCC commands after SETDASA.
> >   
> I agree, what I meant by "SETDASA is simply faster than ENTDAA, but
> only if there is no need to collect BCR/DCR/PID of such devices." Is
> that it is faster than DAA but only if not followed by GET CCC
> commands to gather BCR/DCR/PID. I think we are on the same page here.

Yes, but right now it's not the case, see my other reply ;-).

> 
> > But that's also my understanding that ENTDAA should always work, and
> > SETDASA usage is only needed if you want to reserve a dynamic
> > address and assign it to a device before DAA takes place. This way
> > you can enforce the device priority (WRT IBIs). But honestly,
> > that's the only use case I can think of, and to me, it sounds like
> > an advanced feature we may want to support at some point, but don't
> > need in the initial implementation. 
> Still ENTDAA seems to be sufficient for IBI prioritization but I can
> imagine some use cases where people would like to use it for such
> purposes. Note that SETDASA is applicable only for devices with SA so
> it is self-explanatory that it cannot be considered as utility to
> define priorities for all devices before ENTDAA. 

We have SETNEWDA for other use cases: say you want one of your device to
have an higher priority, you can just manually set a new dynamic
address that is lower than any other devices on the bus (I plan to
expose that through sysfs, by making the address file writable).

-- 
Boris Brezillon, Bootlin (formerly Free Electrons)
Embedded Linux and Kernel engineering
https://bootlin.com