linux-kernel - Re: [PATCH 03/16] tty: serial: 8250_core: read only RX if there is something in the FIFO

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Date:	Thu, 12 Feb 2015 09:40:20 +0000
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc:	Peter Hurley <peter@...leysoftware.com>,
	Tony Lindgren <tony@...mide.com>,
	Nicolas Schichan <nschichan@...ebox.fr>,
	gregkh@...uxfoundation.org, linux-kernel@...r.kernel.org,
	balbi@...com, linux-serial@...r.kernel.org,
	linux-omap@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 03/16] tty: serial: 8250_core: read only RX if there is
 something in the FIFO

On Thu, Feb 12, 2015 at 09:45:38AM +0100, Sebastian Andrzej Siewior wrote:
> On 02/11/2015 09:42 PM, Peter Hurley wrote:
> 
> >> Reverting makes sense to me if it has caused a regression. Maybe Sebastian
> >> can update his patch to do this based on some quirk flag instead?
> > 
> > That's fine with me. There's a 'bugs' field in struct 8250_uart_port and
> > UART_BUG_* defines in 8250/8250.h for that purpose.
> 
> Makes sense. Reading an empty FIFO does not look right. Maybe we should
> do the bug flag the other way around? But I can do what I am told to so
> if there is more fallout than just this Marvell UART I could come
> around with a patch to the bug field for the older OMAP.

Reading the RX FIFO is something that goes back a long time in the 8250
driver, to the time when Ted Ts'o wrote the driver.

I would suggest that it remains there as the default (it was obviously
found to be necessary for x86 all those years ago when Linux was in
its infancy) and has survived for getting on 20 years without issue.

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