linux-kernel - Re: [PATCH v3 0/5] Introduce i3c device userspace interface

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Date:   Wed, 19 Feb 2020 09:16:58 +0100
From:   Boris Brezillon <boris.brezillon@...labora.com>
To:     Vitor Soares <Vitor.Soares@...opsys.com>
Cc:     "bbrezillon@...nel.org" <bbrezillon@...nel.org>,
        Joao Pinto <Joao.Pinto@...opsys.com>,
        Jose Abreu <Jose.Abreu@...opsys.com>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "wsa@...-dreams.de" <wsa@...-dreams.de>,
        "arnd@...db.de" <arnd@...db.de>,
        "broonie@...nel.org" <broonie@...nel.org>,
        "corbet@....net" <corbet@....net>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-i3c@...ts.infradead.org" <linux-i3c@...ts.infradead.org>
Subject: Re: [PATCH v3 0/5] Introduce i3c device userspace interface

On Wed, 19 Feb 2020 00:39:31 +0000
Vitor Soares <Vitor.Soares@...opsys.com> wrote:

> Hi Boris,
> 
> From: Vitor Soares <vitor.soares@...opsys.com>
> Date: Wed, Feb 19, 2020 at 00:20:38
> 
> > For today there is no way to use i3c devices from user space and
> > the introduction of such API will help developers during the i3c device
> > or i3c host controllers development.
> > 
> > The i3cdev module is highly based on i2c-dev and yet I tried to address
> > the concerns raised in [1].
> > 
> > NOTES:
> > - The i3cdev dynamically request an unused major number.
> > 
> > - The i3c devices are dynamically exposed/removed from dev/ folder based
> >   on if they have a device driver bound to it.
> > 
> > - For now, the module exposes i3c devices without device driver on
> >   dev/bus/i3c/<bus>-<pid>
> > 
> > - As in the i2c subsystem, here it is exposed the i3c_priv_xfer to
> >   userspace. I tried to use a dedicated structure as in spidev but I don't
> >   see any obvious advantage.
> > 
> > - Since the i3c API only exposes i3c_priv_xfer to devices, for now, the
> >   module just makes use of one ioctl(). This can change in the future with
> >   the introduction hdr commands or by the need of exposing some CCC
> >   commands to the device API (private contract between master-slave).
> >   Regarding the i3c device info, some information is already available
> >   through sysfs. We can add more device attributes to expose more
> >   information or add a dedicated ioctl() request for that purpose or both.
> > 
> > - Similar to i2c, I have also created a tool that you can find in [2]
> >   for testing purposes. If you have some time available I would appreciate
> >   your feedback about it as well.
> > 
> > [1] https://lkml.org/lkml/2018/11/15/853
> > [2] https://github.com/vitor-soares-snps/i3c-tools.git
> > 
> > Changes in v3:
> >   Use the xfer_lock to prevent device detach during ioctl call
> >   Expose i3cdev under /dev/bus/i3c/ folder like usb does
> >   Change NOTIFY_BOUND to NOTIFY_BIND, this allows the device detach occur
> >   before driver->probe call
> >   Avoid use of IS_ERR_OR_NULL
> >   Use u64_to_user_ptr instead of (void __user *)(uintptr_t) cast
> >   Allocate k_xfer and data_ptrs at once and eliminate double allocation
> >   check
> >   Pass i3cdev to dev->driver_data
> >   Make all minors available
> >   Add API documentation
> > 
> > Changes in v2:
> >   Use IDR api for minor numbering
> >   Modify ioctl struct
> >   Fix SPDX license
> > 
> > Vitor Soares (5):
> >   i3c: master: export i3c_masterdev_type
> >   i3c: master: export i3c_bus_type symbol
> >   i3c: master: add i3c_for_each_dev helper
> >   i3c: add i3cdev module to expose i3c dev in /dev
> >   userspace-api: add i3cdev documentation
> > 
> >  Documentation/userspace-api/i3c/i3cdev.rst | 116 ++++++++
> >  drivers/i3c/Kconfig                        |  15 +
> >  drivers/i3c/Makefile                       |   1 +
> >  drivers/i3c/i3cdev.c                       | 429 +++++++++++++++++++++++++++++
> >  drivers/i3c/internals.h                    |   2 +
> >  drivers/i3c/master.c                       |  16 +-
> >  include/uapi/linux/i3c/i3cdev.h            |  38 +++
> >  7 files changed, 616 insertions(+), 1 deletion(-)
> >  create mode 100644 Documentation/userspace-api/i3c/i3cdev.rst
> >  create mode 100644 drivers/i3c/i3cdev.c
> >  create mode 100644 include/uapi/linux/i3c/i3cdev.h
> > 
> > -- 
> > 2.7.4  
> 
> I want to make you know that none of your previous comments was ignored 
> and  I would like to start the discussion from this point.

Sure, np. I'll probably wait for a v4 exploring the option I proposed
then.