diff mbox series

[v2,2/2] earlycon: Let users set the clock frequency

Message ID 20221123-serial-clk-v2-2-9c03ce8940d8@chromium.org
State New
Headers show
Series earlycon: Let users set the clock frequency | expand

Commit Message

Ricardo Ribalda Nov. 24, 2022, 10:02 a.m. UTC 
Some platforms, namely AMD Picasso, use non standard uart clocks (48M),
witch makes it impossible to use with earlycon.

Let the user select its own frequency.

Signed-off-by: Ricardo Ribalda <ribalda@chromium.org>
diff mbox series

Patch

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index a465d5242774..9efb6c3b0486 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -1182,10 +1182,10 @@ 
 			specified, the serial port must already be setup and
 			configured.
 
-		uart[8250],io,<addr>[,options]
-		uart[8250],mmio,<addr>[,options]
-		uart[8250],mmio32,<addr>[,options]
-		uart[8250],mmio32be,<addr>[,options]
+		uart[8250],io,<addr>[,options[,uartclk]]
+		uart[8250],mmio,<addr>[,options[,uartclk]]
+		uart[8250],mmio32,<addr>[,options[,uartclk]]
+		uart[8250],mmio32be,<addr>[,options[,uartclk]]
 		uart[8250],0x<addr>[,options]
 			Start an early, polled-mode console on the 8250/16550
 			UART at the specified I/O port or MMIO address.
@@ -1194,7 +1194,9 @@ 
 			If none of [io|mmio|mmio32|mmio32be], <addr> is assumed
 			to be equivalent to 'mmio'. 'options' are specified
 			in the same format described for "console=ttyS<n>"; if
-			unspecified, the h/w is not initialized.
+			unspecified, the h/w is not initialized. 'uartclk' is
+			the uart clock frequency; if unspecified, it is set
+			to 'BASE_BAUD' * 16.
 
 		pl011,<addr>
 		pl011,mmio32,<addr>
diff --git a/drivers/tty/serial/earlycon.c b/drivers/tty/serial/earlycon.c
index 5b73da9487b1..2db92d36351b 100644
--- a/drivers/tty/serial/earlycon.c
+++ b/drivers/tty/serial/earlycon.c
@@ -120,9 +120,15 @@  static int __init parse_options(struct earlycon_device *device, char *options)
 	}
 
 	if (options) {
+		char *uartclk;
+
 		if (kstrtouint(options, 0, &device->baud) < 0)
 			pr_warn("[%s] unsupported earlycon baud rate option\n",
 				options);
+		uartclk = strchr(options, ',');
+		if (uartclk && kstrtouint(uartclk, 0, &port->uartclk) < 0)
+			pr_warn("[%s] unsupported earlycon uart clkrate option\n",
+				options);
 		length = min(strcspn(options, " ") + 1,
 			     (size_t)(sizeof(device->options)));
 		strscpy(device->options, options, length);
@@ -141,7 +147,8 @@  static int __init register_earlycon(char *buf, const struct earlycon_id *match)
 		buf = NULL;
 
 	spin_lock_init(&port->lock);
-	port->uartclk = BASE_BAUD * 16;
+	if (!port->uartclk)
+		port->uartclk = BASE_BAUD * 16;
 	if (port->mapbase)
 		port->membase = earlycon_map(port->mapbase, 64);