netdev - Re: [PATCH v2 net] ptp: ocp: adjust serial port symlink creation

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Message-ID: <15f59e29-ac03-4018-bbc3-c4ac5a2964db@linux.dev>
Date: Wed, 5 Jun 2024 11:59:30 +0100
From: Vadim Fedorenko <vadim.fedorenko@...ux.dev>
To: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: Jakub Kicinski <kuba@...nel.org>, Jiri Slaby <jirislaby@...nel.org>,
 Jonathan Lemon <jonathan.lemon@...il.com>, linux-serial@...r.kernel.org,
 netdev@...r.kernel.org
Subject: Re: [PATCH v2 net] ptp: ocp: adjust serial port symlink creation

On 05/06/2024 11:41, Greg Kroah-Hartman wrote:
> On Wed, Jun 05, 2024 at 11:14:28AM +0100, Vadim Fedorenko wrote:
>> On 05/06/2024 11:05, Greg Kroah-Hartman wrote:
>>> On Wed, Jun 05, 2024 at 12:53:13AM +0100, Vadim Fedorenko wrote:
>>>> On 04/06/2024 12:50, Greg Kroah-Hartman wrote:
>>>>> On Wed, May 22, 2024 at 01:39:21PM +0100, Vadim Fedorenko wrote:
>>>>>> On 10/05/2024 12:13, Greg Kroah-Hartman wrote:
>>>>>>> On Fri, May 10, 2024 at 11:04:05AM +0000, Vadim Fedorenko wrote:
>>>>>>>> The commit b286f4e87e32 ("serial: core: Move tty and serdev to be children
>>>>>>>> of serial core port device") changed the hierarchy of serial port devices
>>>>>>>> and device_find_child_by_name cannot find ttyS* devices because they are
>>>>>>>> no longer directly attached. Add some logic to restore symlinks creation
>>>>>>>> to the driver for OCP TimeCard.
>>>>>>>>
>>>>>>>> Fixes: b286f4e87e32 ("serial: core: Move tty and serdev to be children of serial core port device")
>>>>>>>> Signed-off-by: Vadim Fedorenko <vadim.fedorenko@...ux.dev>
>>>>>>>> ---
>>>>>>>> v2:
>>>>>>>>      add serial/8250 maintainers
>>>>>>>> ---
>>>>>>>>      drivers/ptp/ptp_ocp.c | 30 +++++++++++++++++++++---------
>>>>>>>>      1 file changed, 21 insertions(+), 9 deletions(-)
>>>>>>>
>>>>>>> Hi,
>>>>>>>
>>>>>>> This is the friendly patch-bot of Greg Kroah-Hartman.  You have sent him
>>>>>>> a patch that has triggered this response.  He used to manually respond
>>>>>>> to these common problems, but in order to save his sanity (he kept
>>>>>>> writing the same thing over and over, yet to different people), I was
>>>>>>> created.  Hopefully you will not take offence and will fix the problem
>>>>>>> in your patch and resubmit it so that it can be accepted into the Linux
>>>>>>> kernel tree.
>>>>>>>
>>>>>>> You are receiving this message because of the following common error(s)
>>>>>>> as indicated below:
>>>>>>>
>>>>>>> - You have marked a patch with a "Fixes:" tag for a commit that is in an
>>>>>>>       older released kernel, yet you do not have a cc: stable line in the
>>>>>>>       signed-off-by area at all, which means that the patch will not be
>>>>>>>       applied to any older kernel releases.  To properly fix this, please
>>>>>>>       follow the documented rules in the
>>>>>>>       Documentation/process/stable-kernel-rules.rst file for how to resolve
>>>>>>>       this.
>>>>>>>
>>>>>>> If you wish to discuss this problem further, or you have questions about
>>>>>>> how to resolve this issue, please feel free to respond to this email and
>>>>>>> Greg will reply once he has dug out from the pending patches received
>>>>>>> from other developers.
>>>>>>
>>>>>> Hi Greg!
>>>>>>
>>>>>> Just gentle ping, I'm still looking for better solution for serial
>>>>>> device lookup in TimeCard driver.
>>>>>
>>>>> See my comment on the other patch in this thread.
>>>>>
>>>>> In short, you shouldn't need to do any of this.
>>>>
>>>> Got it, thanks. I'll try to find another way.
>>>
>>> Wait, no, please just remove all that, it should not be needed at all.
>>
>> Do you mean remove symlinks from the driver? We have open-source
>> user-space software which relies on them to discover proper devices. If
>> I remove symlinks it will break the software.
> 
> the symlinks should be done in userspace in the /dev/serial/ directory,
> why would userspace need to know the symlink of the serial device in
> a sysfs tree?  What exactly are you trying to represent here that
> requires this to be a custom thing?

Well, the hardware exposes up to 4 different serial ports for different
functions. And only driver knows which feature is attached to which port
because of differences in the HW. There is no way for user-space to get
this information on it's own. And one more thing, some HW versions
expose special attributes in sysfs consumed by the same software.
And there are setups with several boards in the system. Currently we
separate them by providing different sysfs entries only, the software
then figures all details automatically.

Thanks,
Vadim