linux-kernel - Re: [PATCH 5/5] Documentation: Add ABI doc for attributes of LJCA device

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Date:   Fri, 24 Feb 2023 11:53:08 +0100
From:   Linus Walleij <linus.walleij@...aro.org>
To:     Ye Xiang <xiang.ye@...el.com>
Cc:     Lee Jones <lee@...nel.org>, Wolfram Sang <wsa@...nel.org>,
        Tyrone Ting <kfting@...oton.com>,
        Mark Brown <broonie@...nel.org>,
        Bartosz Golaszewski <brgl@...ev.pl>, linux-i2c@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-spi@...r.kernel.org,
        linux-gpio@...r.kernel.org, srinivas.pandruvada@...el.com,
        heikki.krogerus@...ux.intel.com, andriy.shevchenko@...ux.intel.com,
        sakari.ailus@...ux.intel.com, zhifeng.wang@...el.com,
        wentong.wu@...el.com, lixu.zhang@...el.com
Subject: Re: [PATCH 5/5] Documentation: Add ABI doc for attributes of LJCA device

Hi Ye,

thanks for your patch!

On Sun, Feb 19, 2023 at 7:31 PM Ye Xiang <xiang.ye@...el.com> wrote:

> Add sysfs attributes Documentation entries for LJCA device
>
> Signed-off-by: Ye Xiang <xiang.ye@...el.com>
(...)
> +What:          /sys/bus/usb/.../cmd
> +Date:          July 2023
> +KernelVersion: 6.4
> +Contact:       Ye Xiang <xiang.ye@...el.com>
> +Description:
> +               Commands supported by LJCA device.
> +               When read, it will return valid commands.
> +               When write with a command, it will execute the command.
> +               Valid commands are [dfu, reset, debug]
> +               dfu:    Force LJCA device to enter DFU mode.
> +               reset:  Trigger soft reset for LJCA device.
> +               debug:  Enable debug logging.

Given that there are kernel drivers for this device, it looks pretty
dangerous to make it possible for userspace to reset the device?

But maybe it will re-enumerate when you do this so all drivers
unload cleanly and then re-probe?

I guess the DFU mode will use the USB standard class for updating
the firmware?

Perhaps a short blurb on the use case for each string could be
helpful, like "echo dfu to this file so as to put the device into
DFU mode so the firmware can be updated".

Is the idea that e.g. fwupdmgr should provide a front-end for this?

Yours,
Linus Walleij