linux-kernel - Re: [PATCH 4.19 144/245] serial: uartps: Wait for tx

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Message-ID: <20200930200711.GA22586@amd>
Date:   Wed, 30 Sep 2020 22:07:12 +0200
From:   Pavel Machek <pavel@...x.de>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Raviteja Narayanam <raviteja.narayanam@...inx.com>,
        Shubhrajyoti Datta <shubhrajyoti.datta@...inx.com>,
        Sasha Levin <sashal@...nel.org>
Subject: Re: [PATCH 4.19 144/245] serial: uartps: Wait for tx_empty in
 console setup

Hi!

> From: Raviteja Narayanam <raviteja.narayanam@...inx.com>
> 
> [ Upstream commit 42e11948ddf68b9f799cad8c0ddeab0a39da33e8 ]
> 
> On some platforms, the log is corrupted while console is being
> registered. It is observed that when set_termios is called, there
> are still some bytes in the FIFO to be transmitted.
> 
> So, wait for tx_empty inside cdns_uart_console_setup before calling
> set_termios.

> @@ -1246,6 +1247,13 @@ static int cdns_uart_console_setup(struct console *co, char *options)
>  	if (options)
>  		uart_parse_options(options, &baud, &parity, &bits, &flow);
>  
> +	/* Wait for tx_empty before setting up the console */
> +	time_out = jiffies + usecs_to_jiffies(TX_TIMEOUT);
> +
> +	while (time_before(jiffies, time_out) &&
> +	       cdns_uart_tx_empty(port) != TIOCSER_TEMT)
> +		cpu_relax();
> +

So this is spinning for half a second. Could we use msleep(1) instead
of cpu_relax or something like that?

Best regards,
									Pavel

-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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