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Subject: Re: [PATCH v1] serdev: Add interface serdev_device_ioctl
To:     Greg KH <gregkh@linuxfoundation.org>
Cc:     robh@kernel.org, jirislaby@kernel.org,
        linux-serial@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-bluetooth@vger.kernel.org, Zijun Hu <quic_zijuhu@quicinc.com>
References: <1635753048-5289-1-git-send-email-zijuhu@codeaurora.org>
 <YX+eRgCrUs2Y5iaX@kroah.com>
From:   Zijun Hu <zijuhu@codeaurora.org>
Message-ID: <fe5a8bec-b186-c719-5f02-a0a67eb8862f@codeaurora.org>
Date:   Mon, 1 Nov 2021 16:29:10 +0800
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On 11/1/2021 3:59 PM, Greg KH wrote:
> On Mon, Nov 01, 2021 at 03:50:48PM +0800, Zijun Hu wrote:
>> From: Zijun Hu <quic_zijuhu@quicinc.com>
>>
>> For serdev_device which is mounted at virtual tty port, tty ioctl()
>> maybe be used to make serdev_device ready to talk with tty port, so
>> add interface serdev_device_ioctl().
>>
>> Signed-off-by: Zijun Hu <quic_zijuhu@quicinc.com>
>> ---
>>  drivers/tty/serdev/core.c           | 11 +++++++++++
>>  drivers/tty/serdev/serdev-ttyport.c | 12 ++++++++++++
>>  include/linux/serdev.h              |  9 +++++++++
>>  3 files changed, 32 insertions(+)
>>
>> diff --git a/drivers/tty/serdev/core.c b/drivers/tty/serdev/core.c
>> index f1324fe99378..c0f6cd64716b 100644
>> --- a/drivers/tty/serdev/core.c
>> +++ b/drivers/tty/serdev/core.c
>> @@ -405,6 +405,17 @@ int serdev_device_set_tiocm(struct serdev_device *serdev, int set, int clear)
>>  }
>>  EXPORT_SYMBOL_GPL(serdev_device_set_tiocm);
>>  
>> +int serdev_device_ioctl(struct serdev_device *serdev, unsigned int cmd, unsigned long arg)
>> +{
>> +	struct serdev_controller *ctrl = serdev->ctrl;
>> +
>> +	if (!ctrl || !ctrl->ops->ioctl)
>> +		return -EOPNOTSUPP;
> 
> Wrong error for returning that an ioctl is not handled :(
checkpatch.pl always reports below WARNING when i use ENOTSUPP as present interfaces
do. so i change error code to EOPNOTSUPP.

#28: FILE: drivers/tty/serdev/core.c:412:
+               return -ENOTSUPP;

WARNING: ENOTSUPP is not a SUSV4 error code, prefer EOPNOTSUPP
> 
> Anyway, what in-tree driver needs this functionality?  Why does serdev
> need any ioctl commands?
>
i am developing driver for a special bluetooth controller which is integrated within SOC,
and it does not connect with the BT HOST with UART as normal controller do, but it has very
similar features as the BT controller with UART I/F. it is mounted on a virtual serial port
driven by a tty driver developed. but it need to call tty ioctl to make the 
special BT controller ready to talk with tty port. so i add this interface.

as you known, the main purpose of ioctl is to achieve MISC and irregular control. so it is useful
for these irregular devices.
 
thanks  
> thanks,
> 
> greg k-h
>