linux-kernel - [PATCH 2/2] serial: earlycon: allow to specify uartclk in earlycon kernel-parameter

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Date:	Mon, 19 Oct 2015 14:40:24 +0900
From:	Masahiro Yamada <yamada.masahiro@...ionext.com>
To:	linux-serial@...r.kernel.org
Cc:	Masahiro Yamada <yamada.masahiro@...ionext.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	linux-kernel@...r.kernel.org, Jiri Slaby <jslaby@...e.com>
Subject: [PATCH 2/2] serial: earlycon: allow to specify uartclk in earlycon kernel-parameter

The input clock frequency varies from device to device, but the
earlycon uses the fixed frequency (BASE_BAUD * 16).  It makes
impossible to set the correct divisor to the register.

This commit allows to specify the input clock frequency from the
kernel-parameter.

[Example]

    earlycon=uart8250,mmio32,0x43fb0000,115200,12288000

The input clock frequency (12288000, in this case) should be specified
after the baudrate.  If not specified, the default (BASE_BAUD * 16) is
used.

Signed-off-by: Masahiro Yamada <yamada.masahiro@...ionext.com>
---

 drivers/tty/serial/earlycon.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/drivers/tty/serial/earlycon.c b/drivers/tty/serial/earlycon.c
index 07f7393..8030765 100644
--- a/drivers/tty/serial/earlycon.c
+++ b/drivers/tty/serial/earlycon.c
@@ -95,6 +95,13 @@ static int __init parse_options(struct earlycon_device *device, char *options)
 		length = min(strcspn(options, " ") + 1,
 			     (size_t)(sizeof(device->options)));
 		strlcpy(device->options, options, length);
+		options = strchr(options, ',');
+		if (options) {
+			options++;
+			port->uartclk = simple_strtoul(options, NULL, 0);
+		}
+		if (!port->uartclk)
+			port->uartclk = BASE_BAUD * 16;
 	}
 
 	if (port->iotype == UPIO_MEM || port->iotype == UPIO_MEM16 ||
@@ -122,7 +129,6 @@ static int __init register_earlycon(char *buf, const struct earlycon_id *match)
 	if (buf && !parse_options(&early_console_dev, buf))
 		buf = NULL;
 
-	port->uartclk = BASE_BAUD * 16;
 	if (port->mapbase)
 		port->membase = earlycon_map(port->mapbase, 64);
 
-- 
1.9.1

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