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

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Date:   Wed, 19 Feb 2020 00:39:31 +0000
From:   Vitor Soares <Vitor.Soares@...opsys.com>
To:     "bbrezillon@...nel.org" <bbrezillon@...nel.org>
CC:     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>,
        Vitor Soares <Vitor.Soares@...opsys.com>,
        "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

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.

Best regards,
Vitor Soares