linux-kernel - Re: [V3] drivers/tty/serial/qcom-geni-serial: Do stop_rx in suspend path for console if console

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Date:   Fri, 15 Apr 2022 08:59:25 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Vijaya Krishna Nivarthi <quic_vnivarth@...cinc.com>
Cc:     Jiri Slaby <jirislaby@...nel.org>, agross@...nel.org,
        bjorn.andersson@...aro.org, linux-arm-msm@...r.kernel.org,
        linux-serial@...r.kernel.org, linux-kernel@...r.kernel.org,
        quic_msavaliy@...cinc.com, dianders@...omium.org
Subject: Re: [V3] drivers/tty/serial/qcom-geni-serial: Do stop_rx in suspend
 path for console if console_suspend is disabled

On Fri, Apr 08, 2022 at 11:45:11AM +0530, Vijaya Krishna Nivarthi wrote:
> 
> On 4/7/2022 1:21 PM, Jiri Slaby wrote:
> > On 07. 04. 22, 9:25, Vijaya Krishna Nivarthi wrote:
> > > For the case of console_suspend disabled, if back to back suspend/resume
> > > test is executed, at the end of test, sometimes console would appear to
> > > be frozen not responding to input. This would happen because, for
> > > console_suspend disabled, suspend/resume routines only turn resources
> > > off/on but don't do a port close/open.
> > > As a result, during resume, some rx transactions come in before
> > > system is
> > > ready, malfunction of rx happens in turn resulting in console appearing
> > > to be stuck.
> > > 
> > > Do a stop_rx in suspend sequence to prevent this. start_rx is already
> > > present in resume sequence as part of call to set_termios which does a
> > > stop_rx/start_rx.
> > 
> > So why is it OK for every other driver? Should uart_suspend_port() be
> > fixed instead?
> 
> For qcom driver we know that set_termios() call in uart_suspend_port() will
> recover with a call to start_rx.
> However that may not be the case with other drivers.
> 
> We can move stop_rx to uart_suspend_port() and additionally have a start_rx
> in uart_resume_port()
> Please let know if such a change would be ok.

This should not be something that each individual driver has to do,
please fix it for everyone.

thanks,

greg k-h