linux-kernel - Re: [PATCH 3/4] serial: 8250: Handle case port doesn't have TEMT interrupt using em485.

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Message-ID: <20180613175915.279d03e2@alans-desktop>
Date:   Wed, 13 Jun 2018 17:59:38 +0100
From:   Alan Cox <gnomes@...rguk.ukuu.org.uk>
To:     Giulio Benetti <giulio.benetti@...ronovasrl.com>
Cc:     matwey.kornilov@...il.com,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jslaby@...e.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Stefan Potyra <Stefan.Potyra@...ktrobit.com>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        Ed Blake <ed.blake@...drel.com>,
        Joshua Scott <joshua.scott@...iedtelesis.co.nz>,
        Vignesh R <vigneshr@...com>,
        Rolf Evers-Fischer <rolf.evers.fischer@...iv.com>,
        Aaron Sierra <asierra@...-inc.com>,
        Phil Elwell <phil@...pberrypi.org>,
        Rafael Gago <rafael.gago@...il.com>,
        Joel Stanley <joel@....id.au>,
        Sean Wang <sean.wang@...iatek.com>,
        linux-serial@...r.kernel.org (open list:SERIAL DRIVERS),
        linux-kernel@...r.kernel.org (open list)
Subject: Re: [PATCH 3/4] serial: 8250: Handle case port doesn't have TEMT
 interrupt using em485.

> +		} else {
> +			while ((lsr & BOTH_EMPTY) != BOTH_EMPTY) {
> +				lsr = serial_in(p, UART_LSR);
> +				cpu_relax();
> +			}
> +		}

This still needs a timeout in case some kind of hardware flow control line
is asserted and therefore the byte is staying put.

Alan