On 02/01/2015 10:16 PM, Eddie Huang wrote:

Hi Peter,

On Sun, 2015-02-01 at 13:26 -0500, Peter Hurley wrote:

quoted

On 02/01/2015 11:27 AM, Peter Hurley wrote:

quoted

Hi Eddie,

On 01/12/2015 08:08 AM, Eddie Huang wrote:

quoted

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 <redacted>
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 <redacted>
---
 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.

Regards,
Peter Hurley