linux-kernel - Re: [PATCH 4.19 16/52] serial: uartps: Add a timeout to the tx empty wait

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Date:   Thu, 13 Feb 2020 10:29:48 -0800
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Pavel Machek <pavel@...x.de>
Cc:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Jean-Francois Dagenais <jeff.dagenais@...il.com>,
        Shubhrajyoti Datta <shubhrajyoti.datta@...inx.com>,
        Mathieu Poirier <mathieu.poirier@...aro.org>,
        Sasha Levin <sashal@...nel.org>
Subject: Re: [PATCH 4.19 16/52] serial: uartps: Add a timeout to the tx empty
 wait

On Thu, Feb 13, 2020 at 07:22:46PM +0100, Pavel Machek wrote:
> Hi!
> 
> > commit 277375b864e8147975b064b513f491e2a910e66a upstream
> > 
> > In case the cable is not connected then the target gets into
> > an infinite wait for tx empty.
> > Add a timeout to the tx empty wait.
> 
> Was this tested? Because it does not work...
> 
> > Reported-by: Jean-Francois Dagenais <jeff.dagenais@...il.com>
> > Signed-off-by: Shubhrajyoti Datta <shubhrajyoti.datta@...inx.com>
> > Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> > Cc: stable <stable@...r.kernel.org> # 4.19
> > Signed-off-by: Mathieu Poirier <mathieu.poirier@...aro.org>
> > Signed-off-by: Sasha Levin <sashal@...nel.org>
> 
> > @@ -681,16 +683,20 @@ static void cdns_uart_set_termios(struct uart_port *port,
> ...
> > +	int err;
> >  
> >  	spin_lock_irqsave(&port->lock, flags);
> >  
> >  	/* Wait for the transmit FIFO to empty before making changes */
> >  	if (!(readl(port->membase + CDNS_UART_CR) &
> >  				CDNS_UART_CR_TX_DIS)) {
> > -		while (!(readl(port->membase + CDNS_UART_SR) &
> > -				CDNS_UART_SR_TXEMPTY)) {
> > -			cpu_relax();
> > +		err = readl_poll_timeout(port->membase + CDNS_UART_SR,
> > +					 val, (val & CDNS_UART_SR_TXEMPTY),
> > +					 1000, TX_TIMEOUT);
> > +		if (err) {
> > +			dev_err(port->dev, "timed out waiting for tx empty");
> > +			return;
> >  		}
> >  	}
> >
> 
> It will return with lock held and interrupts disabled. Mainline takes
> spinlock later, so it does not have a problem.
> 
> Merging 107475685abfdee504bb0ef4824f15797f6d2d4d before this one
> should fix the problem.

Good catch, that's a mess.  I'll go queue this up now.

greg k-h