Re: [PATCH v2 1/4] tty: serial: Add 8250 earlycon to support noinit option

From: Eddie Huang <eddie.huang@mediatek.com>
To: Peter Hurley <peter@hurleysoftware.com>
Cc: Mark Rutland <mark.rutland@arm.com>,
	linux-doc@vger.kernel.org,
	Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will.deacon@arm.com>, Jiri Slaby <jslaby@suse.cz>,
	Jonathan Corbet <corbet@lwn.net>,
	yh.chen@mediatek.com, Howard Chen <ibanezchen@gmail.com>,
	linux-serial@vger.kernel.org, "Joe.C" <yingjoe.chen@mediatek.com>,
	devicetree@vger.kernel.org,
	Vladimir Murzin <vladimir.murzin@arm.com>,
	Pawel Moll <pawel.moll@arm.com>,
	Ian Campbell <ijc+devicetree@hellion.org.uk>,
	Rob Herring <robh+dt@kernel.org>,
	Matthias Brugger <matthias.bgg@gmail.com>,
	linux-arm-kernel@lists.infradead.org,
	Alan Cox <alan@linux.intel.com>,
	srv_heupstream@mediatek.com,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	linux-kernel@vger.kernel.org,
	Ashwin Chaugule <ashwin.chaugule@linaro.org>,
	Kumar Gala <galak@codeaurora.org>
Subject: Re: [PATCH v2 1/4] tty: serial: Add 8250 earlycon to support noinit option
Date: Mon, 2 Feb 2015 11:16:34 +0800	[thread overview]
Message-ID: <1422846994.5512.25.camel@mtksdaap41> (raw)
In-Reply-To: <54CE6FD9.5030606@hurleysoftware.com>

Hi Peter,

On Sun, 2015-02-01 at 13:26 -0500, Peter Hurley wrote:
> On 02/01/2015 11:27 AM, Peter Hurley wrote:
> > Hi Eddie,
> > 
> > On 01/12/2015 08:08 AM, Eddie Huang wrote:
> >> Add earlycon support not only baudrate option, but also add noinit option.
> >> If use noinit option, 8250 earlycon will not init serial hardware and use
> >> loader setting.
> > 
> > I see this went into Greg's tty-testing branch.
> > 
> > The only point of this is to not program the divisor, right?
> > 
> > I ask because early_serial8250_setup() could already handle this without
> > extra options by simply not doing divisor programming if no baud option is
> > present.
> 
> Does the patch below work for your use-case?
> 
> [ Note: the patch applies to 3.19-rcX. To test, your noinit patches need to be
>   reverted first.
> ]
> 
> --- >% ---
> From: Peter Hurley <peter@hurleysoftware.com>
> Subject: [PATCH] serial: 8250_early: Assume uart already initialized if no
>  baud option
> 
> The <baud><parity><bit> option string is not supplied if the earlycon
> is started via devicetree and OF_EARLYCON_DECLARE(). The option string
> is also not required if started via kernel command line parameters of
> the form:
>   earlycon=uart,mmio,<addr>
>   console=uart,mmio,<addr>
> 
> If earlycon_device->baud is 0, then an option string was not supplied.
> In this case, assume the uart has already been initialized by the
> bootloader or firmware.
> 
> Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
> ---
>  drivers/tty/serial/8250/8250_early.c | 10 ++++++++--
>  1 file changed, 8 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/tty/serial/8250/8250_early.c b/drivers/tty/serial/8250/8250_early.c
> index d7b831b..1701d00 100644
> --- a/drivers/tty/serial/8250/8250_early.c
> +++ b/drivers/tty/serial/8250/8250_early.c
> @@ -149,12 +149,18 @@ static int __init early_serial8250_setup(struct earlycon_device *device,
>  		return 0;
>  
>  	if (!device->baud) {
> +		struct uart_port *port = &device->port;
> +		unsigned int ier;
> +
>  		device->baud = probe_baud(&device->port);
>  		snprintf(device->options, sizeof(device->options), "%u",
>  			 device->baud);
> -	}
>  
> -	init_port(device);
> +		/* assume the device was initialized, only mask interrupts */
> +		ier = serial8250_early_in(port, UART_IER);
> +		serial8250_early_out(port, UART_IER, ier & UART_IER_UUE);
> +	} else
> +		init_port(device);
Should add brace in else.

Where is original line here.
          early_device = device;
>  	device->con->write = early_serial8250_write;
>  	return 0;

With above comment, I test ok on my platform.

Eddie
Best Regards.