linux-kernel - Re: [PATCH v2] USB: serial: xr: Add TIOCGRS485 and TIOCSRS485 ioctls

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Date:   Mon, 13 Mar 2023 12:47:17 +0200
From:   Jarkko Sonninen <kasper@....fi>
To:     Oliver Neukum <oneukum@...e.com>
Cc:     Johan Hovold <johan@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] USB: serial: xr: Add TIOCGRS485 and TIOCSRS485 ioctls

     Hello,

It uses only one flag from the struct from user. Would it be better to 
store only that to state ?

Do I need locking at all in that case ?

The whole struct is stored just in case, if someone would implement 
other functionality later.

     - Jarkko


Oliver Neukum kirjoitti 13/03/2023 klo 11.54:
>
>
> On 13.03.23 09:27, Jarkko Sonninen wrote:
>> Add support for RS-485 in Exar USB adapters.
>> RS-485 mode is controlled by TIOCGRS485 and TIOCSRS485 ioctls.
>> Gpio mode register is set to enable RS-485.
>>
>> Signed-off-by: Jarkko Sonninen <kasper@....fi>
>
>
> Hi,
>
> I am sorry, but locking is really broken here. All these contexts can 
> sleep.
> There is no need for a spinlock. As far as you need locking, just use 
> a mutex.
>
> Secondly, if xr_set_rs485_config() needs locking, so will 
> xr_get_rs485_config()
> or you can get the case that you return half a new and half an old 
> state to user
> space.
>
>     Regards
>         Oliver