earlycon: Let users set the clock frequency

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>
Reviewed-by: Jiri Slaby <jirislaby@kernel.org>
Link: https://lore.kernel.org/r/20221123-serial-clk-v3-1-49c516980ae0@chromium.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 6cfa6e3..b50bdee 100644 (file)
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -1195,10 +1195,10 @@
                        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.
@@ -1207,7 +1207,9 @@
                        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 4f6e9bf..a5fbb6e 100644 (file)
--- a/drivers/tty/serial/earlycon.c
+++ b/drivers/tty/serial/earlycon.c
@@ -120,7 +120,13 @@ static int __init parse_options(struct earlycon_device *device, char *options)
        }
 
        if (options) {
+               char *uartclk;
+
                device->baud = simple_strtoul(options, NULL, 0);
+               uartclk = strchr(options, ',');
+               if (uartclk && kstrtouint(uartclk + 1, 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);
@@ -139,7 +145,8 @@ 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);