linux-kernel - Re: [PATCH v2] serial: 8250_bcm7271: Save/restore RTS in suspend/resume

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Date:   Mon, 4 Jul 2022 08:35:57 -0700
From:   Florian Fainelli <f.fainelli@...il.com>
To:     Jiri Slaby <jirislaby@...nel.org>,
        Florian Fainelli <f.fainelli@...il.com>,
        linux-serial@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, Doug Berger <opendmb@...il.com>,
        Al Cooper <alcooperx@...il.com>,
        Broadcom internal kernel review list 
        <bcm-kernel-feedback-list@...adcom.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [PATCH v2] serial: 8250_bcm7271: Save/restore RTS in
 suspend/resume



On 7/3/2022 11:40 PM, Jiri Slaby wrote:
> On 29. 06. 22, 18:02, Florian Fainelli wrote:
>> From: Doug Berger <opendmb@...il.com>
>>
>> Commit 9cabe26e65a8 ("serial: 8250_bcm7271: UART errors after resuming
>> from S2") prevented an early enabling of RTS during resume, but it did
>> not actively restore the RTS state after resume.
>>
>> Fixes: 9cabe26e65a8 ("serial: 8250_bcm7271: UART errors after resuming 
>> from S2")
>> Signed-off-by: Doug Berger <opendmb@...il.com>
>> Signed-off-by: Florian Fainelli <f.fainelli@...il.com>
>> ---
>>   drivers/tty/serial/8250/8250_bcm7271.c | 24 ++++++++++++++++++------
>>   1 file changed, 18 insertions(+), 6 deletions(-)
>>
>> diff --git a/drivers/tty/serial/8250/8250_bcm7271.c 
>> b/drivers/tty/serial/8250/8250_bcm7271.c
>> index 9b878d023dac..b9cea38c8aff 100644
>> --- a/drivers/tty/serial/8250/8250_bcm7271.c
>> +++ b/drivers/tty/serial/8250/8250_bcm7271.c
> ...
>> @@ -1180,7 +1184,15 @@ static int __maybe_unused 
>> brcmuart_resume(struct device *dev)
>>           start_rx_dma(serial8250_get_port(priv->line));
>>       }
>>       serial8250_resume_port(priv->line);
>> -    port->mctrl = priv->saved_mctrl;
>> +
>> +    if (priv->saved_mctrl & TIOCM_RTS) {
>> +        /* Restore RTS */
>> +        spin_lock_irqsave(&port->lock, flags);
>> +        port->mctrl |= TIOCM_RTS;
>> +        spin_unlock_irqrestore(&port->lock, flags);
>> +        port->ops->set_mctrl(port, port->mctrl);
> 
> Calling ->set_mctrl w/o port->lock doesn't look really safe.

Good point, I will check with Doug whether this was intentional and if 
so, why, and if not why should we move it up under the spinlock.

Thanks!
-- 
Florian