linux-kernel - Re: [PATCHv4 2/3] tty/serial: at91: fix hardware handshake with GPIOs

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Date:   Fri, 30 Sep 2016 11:12:30 +0200
From:   Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>
To:     Richard Genoud <richard.genoud@...il.com>
Cc:     Nicolas Ferre <nicolas.ferre@...el.com>,
        Alexandre Belloni <alexandre.belloni@...e-electrons.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Cyrille Pitchen <cyrille.pitchen@...el.com>,
        linux-serial@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCHv4 2/3] tty/serial: at91: fix hardware handshake with GPIOs

Hello Richard,

On Fri, Sep 30, 2016 at 10:58:00AM +0200, Richard Genoud wrote:
> Commit 1cf6e8fc8341 ("tty/serial: at91: fix RTS line management when
> hardware handshake is enabled") broke the hardware handshake when GPIOs
> were used.
> 
> Hardware handshake with GPIOs used to work before this commit because
> the CRTSCTS flag (termios->c_cflag) was set, but not the
> ATMEL_US_USMODE_HWHS flag (controller register) ; so hardware handshake
> enabled, but not handled by the controller.

What does the HWHS flag control? What if only RTS is a gpio and CTS is
not? Or the other way round?

What is the problematic setup? I guess it's RTS and CTS are gpios and
with that setting ATMEL_US_USMODE_HWHS is wrong? What happens if that
happens?

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |