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

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Date:	Sun, 1 Feb 2015 20:28:43 -0800
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	Peter Hurley <peter@...leysoftware.com>
Cc:	Eddie Huang <eddie.huang@...iatek.com>,
	Rob Herring <robh+dt@...nel.org>,
	Mark Rutland <mark.rutland@....com>,
	Matthias Brugger <matthias.bgg@...il.com>,
	devicetree@...r.kernel.org,
	Vladimir Murzin <vladimir.murzin@....com>,
	srv_heupstream@...iatek.com, Pawel Moll <pawel.moll@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Catalin Marinas <catalin.marinas@....com>,
	Jonathan Corbet <corbet@....net>,
	Will Deacon <will.deacon@....com>,
	linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org,
	yh.chen@...iatek.com, Howard Chen <ibanezchen@...il.com>,
	Ashwin Chaugule <ashwin.chaugule@...aro.org>,
	linux-serial@...r.kernel.org, Kumar Gala <galak@...eaurora.org>,
	"Joe.C" <yingjoe.chen@...iatek.com>, Jiri Slaby <jslaby@...e.cz>,
	linux-arm-kernel@...ts.infradead.org,
	Alan Cox <alan@...ux.intel.com>
Subject: Re: [PATCH v2 1/4] tty: serial: Add 8250 earlycon to support noinit
 option

On Sun, Feb 01, 2015 at 10:45:12PM -0500, Peter Hurley wrote:
> On 02/01/2015 10:16 PM, Eddie Huang wrote:
> > 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@...leysoftware.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@...leysoftware.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.
> 
> I don't do that unless I have to.
> 
> > Where is original line here.
> >           early_device = device;
> 
> Whoops :)
> 
> I wrote the patch from a private branch which implements extensible console
> matching (so a console can define its own match function) and a bunch of
> other console cleanup and code removal. In that series, early_device becomes
> unnecessary and is removed.
> 
> I'll respin proper patches on top of Greg's tty-testing branch with reverts
> for the noinit options. I noticed that one of the noinit patches actually
> has the linkage for the mtk earlycon, so I'll be sure to preserve that.

I can just drop the patches in the tty-testing branch, that's what it is
there for :)

Just let me know the specific patches and I will do so, thanks.

greg k-h
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