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

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Date:   Sat, 25 Feb 2023 02:01:20 +0800
From:   "Ye, Xiang" <xiang.ye@...el.com>
To:     Linus Walleij <linus.walleij@...aro.org>
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 Walleij,

Thanks for the review.

On Fri, Feb 24, 2023 at 11:53:08AM +0100, Linus Walleij wrote:
> 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?
Agree. I would just remove the reset cmd on the next version.
User access LJCA will fail during reset because the reset cmd
could cause LJCA down for a short time.

> 
> But maybe it will re-enumerate when you do this so all drivers
> unload cleanly and then re-probe?
No, I haven't implemented the re-probe yet. It seems quite complicated to
make sure all drivers depend on LJCA re-init. So, I would just stop
exporting the reset interface to userspace.
> 
> I guess the DFU mode will use the USB standard class for updating
> the firmware?
Yes.
> 
> 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".
Thanks will add this blurb.
> 
> Is the idea that e.g. fwupdmgr should provide a front-end for this?
We haven't implemented a front-end in fwupdmgr. dfu-util is used to
update LJCA firmware manually currently. Maybe we will consider
implementing this in fwupdmgr later.
> 
> Yours,
> Linus Walleij

--
Thanks
Ye Xiang