linux-kernel - Re: [PATCH] Enable console on PCI serial devices

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Date:	Fri, 17 Oct 2008 09:36:52 -0600
From:	n0ano@...no.com
To:	Bjorn Helgaas <bjorn.helgaas@...com>
Cc:	n0ano@...no.com, Alan Cox <alan@...rguk.ukuu.org.uk>,
	donald.d.dugger@...el.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Enable console on PCI serial devices

On Fri, Oct 17, 2008 at 08:46:40AM -0600, Bjorn Helgaas wrote:
>... 
> this text is a little confusing.  Since you multiply by 16 below, the
> number specified by the user isn't really the crystal frequency, is it?

Can't argue with that.  How about this patch which describes the
parameter more acurately as a multiplier.

Signed-off-by: Don Dugger <donald.d.dugger@...el.com>

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 82c561f..6e5334d 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -505,12 +505,15 @@ and is between 256 and 4096 characters. It is defined in the file
 			Documentation/networking/netconsole.txt for an
 			alternative.
 
-		uart[8250],io,<addr>[,options]
-		uart[8250],mmio,<addr>[,options]
+		uart[8250],io,<addr>[,options[,mult]]
+		uart[8250],mmio,<addr>[,options[,mult]]
 			Start an early, polled-mode console on the 8250/16550
 			UART at the specified I/O port or MMIO address,
 			switching to the matching ttyS device later.  The
-			options are the same as for ttyS, above.
+			"options" are the same as for ttyS, above.  "mult"
+			is a multiplier defining the crystal frequency which
+			defaults to 115200 (typically the fastest baud rate
+			supported by the uart).
 
                 If the device connected to the port is not a TTY but a braille
                 device, prepend "brl," before the device type, for instance
@@ -518,8 +521,8 @@ and is between 256 and 4096 characters. It is defined in the file
 		For now, only VisioBraille is supported.
 
 	earlycon=	[KNL] Output early console device and options.
-		uart[8250],io,<addr>[,options]
-		uart[8250],mmio,<addr>[,options]
+		uart[8250],io,<addr>[,options,[mult]]
+		uart[8250],mmio,<addr>[,options,[mult]]
 			Start an early, polled-mode console on the 8250/16550
 			UART at the specified I/O port or MMIO address.
 			The options are the same as for ttyS, above.
diff --git a/drivers/serial/8250_early.c b/drivers/serial/8250_early.c
index f279745..edd5803 100644
--- a/drivers/serial/8250_early.c
+++ b/drivers/serial/8250_early.c
@@ -180,6 +180,11 @@ static int __init parse_options(struct early_serial8250_device *device,
 		snprintf(device->options, sizeof(device->options), "%u",
 			device->baud);
 	}
+	options = strchr(options, ',');
+	if (options) {
+		options++;
+		port->uartclk = simple_strtoul(options, NULL, 0) * 16;
+	}
 
 	printk(KERN_INFO "Early serial console at %s 0x%llx (options '%s')\n",
 		mmio ? "MMIO" : "I/O port",
--
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