linux-kernel - Re: [PATCH v3] tty: resolve loopback wait problem for aging serial port

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Message-ID: <X/LbMCeNbjedkIiy@hovoldconsulting.com>
Date:   Mon, 4 Jan 2021 10:09:04 +0100
From:   Johan Hovold <johan@...nel.org>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     zhangqiumiao1@...wei.com, jirislaby@...nel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] tty: resolve loopback wait problem for aging serial
 port

On Wed, Dec 30, 2020 at 02:57:14PM +0100, Greg Kroah-Hartman wrote:
> On Wed, Dec 30, 2020 at 09:45:29PM +0800, zhangqiumiao1@...wei.com wrote:
> > From: Qiumiao Zhang <zhangqiumiao1@...wei.com>
> > 
> > Because serial port is low-speed device, serial port writing will be suspended
> > when the buffer of driver layer is full due to serial port aging.
> 
> What do you mean here exactly?  What is "serial port aging"?
> 
> And since when is a serial port a low-speed device?  Compared to what?
> 
> > The concrete
> > representation is n_tty_write blocking in the process of wait_woken, the process
> > of writing serial port exists without feedback, and becomes a zombie process.
> 
> I do not understand this sentance, sorry.  Can you rephrase it?
> 
> > So for serial port, set the timeout value of wait_woken function to 60s. Wake up
> > and flush the buffer after timeout.
> 
> Where did the 60 second number come from?  Why that value and not any
> other specific value?
> 
> 
> > 
> > Signed-off-by: Qiumiao Zhang <zhangqiumiao1@...wei.com>
> > ---
> > v3:
> >  add changes from v1 to v2
> > 
> > v2:
> >  change to use "real name"
> >  fix wrong expression in path description
> >  remove config option
> >  use driver type to judge tty device type

Note that no mails from zhangqiumiao1@...wei.com appears to make it to
the lists so anyone not in CC only sees your replies, Greg. 

Qiumiao Zhang, you need to check your mail setup so that you can post to
the lists.

Johan