linux-kernel - Re: [PATCH v10 0/9] Add the I3C subsystem

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Date:   Thu, 15 Nov 2018 15:18:21 +0000
From:   vitor <vitor.soares@...opsys.com>
To:     Boris Brezillon <boris.brezillon@...tlin.com>,
        vitor <vitor.soares@...opsys.com>
CC:     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>,
        <linux-gpio@...r.kernel.org>, Sekhar Nori <nsekhar@...com>,
        Przemyslaw Gaj <pgaj@...ence.com>,
        Peter Rosin <peda@...ntia.se>,
        Mike Shettel <mshettel@...eaurora.org>,
        Stephen Boyd <swboyd@...omium.org>,
        Mark Brown <broonie@...nel.org>
Subject: Re: [PATCH v10 0/9] Add the I3C subsystem

Hi,

On 15/11/18 12:57, Boris Brezillon wrote:
> +Mark Brown for the question about /dev/spidev
>
> Hi Vitor,
>
> On Thu, 15 Nov 2018 12:14:37 +0000
> vitor <vitor.soares@...opsys.com> wrote:
>
>> Hi Boris,
>>
>> Given the current state of the subsystem I think it might worth start to
>> think how to expose the devices under /dev.
> Thanks for starting this discussion. I'm not against the idea in
> general, we just need to be careful when doing that.
>
>> My initial thoughts are to do the same think as for i2c, expose the
>> buses or the i3c_devices and use ioctl for private transfers.
> Exposing the bus is dangerous IMO, because an I3C bus is not like an
> I2C bus:
>
>     * I3C device needs to be discovered through DAA
>     * I2C devices need to be declared ahead of time, and LVR is used to
>       determine the limitations on the bus at runtime
>
> So you'd anyway be able to interact only with devices that have
> previously been discovered.
>
> Note that the virtual I2C bus is already exposed, but any command
> targeting an address that is not attached to a registered I2C dev will
> get a -ENOENT error.
I initially thought to do the same thing for the i3c devices adding a 
routine get_i3c_dev_by_addr()...
>
> What we could do though, is expose I3C devices that do not have a
> driver in kernel space, like spidev does.

...but I like more this approach.

>> Some
>> direct CCC commands can be sent through the /sys as you plan for SETNEWDA .
> Yes, CCC commands that need to be exposed to userspace should be
> exposed through sysfs, or, if we decide to create a /dev/i3cX device
> per bus, through ioctls.

There already some attributes exposed, just need to add the possibility 
to write to them and off course add some that are missing like GETSTATUS.

>
>> What do you think about this?
> I think this request is perfectly valid, we just need to decide how it
> should be done, and before we take this decision, I'd like to get
> inputs from other maintainers.
>
> Mark, Wolfram, Arnd, Greg, any opinion?
>
> Regards,
>
> Boris


Best regards,

Vitor Soares