From mboxrd@z Thu Jan 1 00:00:00 1970 From: peter@hurleysoftware.com (Peter Hurley) Date: Sun, 01 Feb 2015 13:26:33 -0500 Subject: [PATCH v2 1/4] tty: serial: Add 8250 earlycon to support noinit option In-Reply-To: <54CE53F3.5040709@hurleysoftware.com> References: <1421068104-30463-1-git-send-email-eddie.huang@mediatek.com> <1421068104-30463-2-git-send-email-eddie.huang@mediatek.com> <54CE53F3.5040709@hurleysoftware.com> Message-ID: <54CE6FD9.5030606@hurleysoftware.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org 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 Subject: [PATCH] serial: 8250_early: Assume uart already initialized if no baud option The 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, console=uart,mmio, 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 --- 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); device->con->write = early_serial8250_write; return 0; -- 2.2.2