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

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Message-ID: <e42527f9-fa5e-f03d-3af8-fe2c27f9597b@quicinc.com>
Date:   Fri, 8 Apr 2022 11:45:11 +0530
From:   Vijaya Krishna Nivarthi <quic_vnivarth@...cinc.com>
To:     Jiri Slaby <jirislaby@...nel.org>, <agross@...nel.org>,
        <bjorn.andersson@...aro.org>, <gregkh@...uxfoundation.org>,
        <linux-arm-msm@...r.kernel.org>, <linux-serial@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
CC:     <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 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.
Thank you.