linux-kernel - Re: [PATCH v1] serdev: Add interface serdev_device

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Date:   Mon, 1 Nov 2021 12:18:20 +0100
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Zijun Hu <zijuhu@...eaurora.org>
Cc:     robh@...nel.org, jirislaby@...nel.org,
        linux-serial@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-bluetooth@...r.kernel.org, Zijun Hu <quic_zijuhu@...cinc.com>
Subject: Re: [PATCH v1] serdev: Add interface serdev_device_ioctl

On Mon, Nov 01, 2021 at 05:28:26PM +0800, Zijun Hu wrote:
> 
> 
> On 11/1/2021 4:32 PM, Greg KH wrote:
> > On Mon, Nov 01, 2021 at 04:29:10PM +0800, Zijun Hu wrote:
> >>
> >>
> >> 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@...cinc.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@...cinc.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
> > 
> > Both of them are not the correct error to return when an ioctl is not
> > supported.
> > 
> is ENODEV okay?

No, -ENOTTY is the correct one as per the documentation, right?

> >>> 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.
> > 
> > Please submit this change when you submit your driver that uses it at
> > the same time so we can review them all at once.  We do not add apis
> > that are not used in the kernel tree.
> > 
> okay
> >> as you known, the main purpose of ioctl is to achieve MISC and irregular control. so it is useful
> >> for these irregular devices.
> > 
> > For tty devices, "custom" ioctls are not ok, use the standard tty
> > commands and you should be fine for everything you need to do.
> > 
> > If not, then perhaps your design is incorrect?
> > 
> i just want to refer bt_ioctl within https://source.codeaurora.org/quic/qsdk/oss/kernel/linux-ipq-5.4/tree/drivers/soc/qcom/bt_tty.c?h=NHSS.QSDK.11.5.0.5.r2
> by serdev. so add this interface.

The 5.4 kernel is not relevant here, so I do not understand.

> are there any other good solution to advise?

Why not work with the bluetooth developers on this?

thanks,

greg k-h