* [PATCH v3 1/2] serial: earlycon: add uart_clk_freq parameter
2026-06-15 0:40 [PATCH v3 0/2] ACPI: SPCR: Support UART clock frequency field Markus Probst
@ 2026-06-15 0:40 ` Markus Probst
2026-07-10 12:36 ` Greg Kroah-Hartman
2026-06-15 0:40 ` [PATCH v3 2/2] ACPI: SPCR: Support UART clock frequency field Markus Probst
1 sibling, 1 reply; 5+ messages in thread
From: Markus Probst @ 2026-06-15 0:40 UTC (permalink / raw)
To: Greg Kroah-Hartman, Jiri Slaby, Rafael J. Wysocki, Len Brown
Cc: linux-kernel, linux-serial, linux-acpi, Markus Probst
Add function `setup_earlycon_with_uartclk`. This allows the
options string to be reused with `add_preferred_console`, while still
allowing to set the uart clock frequency. This will be used in the
following commit ("ACPI: SPCR: Support UART clock frequency field").
No logical change intended.
Signed-off-by: Markus Probst <markus.probst@posteo.de>
---
drivers/tty/serial/earlycon.c | 17 ++++++++++++-----
include/linux/serial_core.h | 11 +++++++++--
2 files changed, 21 insertions(+), 7 deletions(-)
diff --git a/drivers/tty/serial/earlycon.c b/drivers/tty/serial/earlycon.c
index ab9af37f6cda..5a20fe9e3fb6 100644
--- a/drivers/tty/serial/earlycon.c
+++ b/drivers/tty/serial/earlycon.c
@@ -135,11 +135,14 @@ static int __init parse_options(struct earlycon_device *device, char *options)
return 0;
}
-static int __init register_earlycon(char *buf, const struct earlycon_id *match)
+static int __init register_earlycon(char *buf, unsigned int uart_clk_freq,
+ const struct earlycon_id *match)
{
int err;
struct uart_port *port = &early_console_dev.port;
+ port->uartclk = uart_clk_freq;
+
/* On parsing error, pass the options buf to the setup function */
if (buf && !parse_options(&early_console_dev, buf))
buf = NULL;
@@ -163,8 +166,9 @@ static int __init register_earlycon(char *buf, const struct earlycon_id *match)
}
/**
- * setup_earlycon - match and register earlycon console
- * @buf: earlycon param string
+ * setup_earlycon_with_uartclk - match and register earlycon console
+ * @buf: earlycon param string
+ * @uart_clk_freq: uart clock frequency in Hz or 0 for BASE_BAUD*16
*
* Registers the earlycon console matching the earlycon specified
* in the param string @buf. Acceptable param strings are of the form
@@ -177,10 +181,13 @@ static int __init register_earlycon(char *buf, const struct earlycon_id *match)
* <options> string in the 'options' parameter; all other forms set
* the parameter to NULL.
*
+ * If the uart clock frequency is specified in the 'options' parameter,
+ * the value of the param @uart_clk_freq will be ignored.
+ *
* Returns 0 if an attempt to register the earlycon was made,
* otherwise negative error code
*/
-int __init setup_earlycon(char *buf)
+int __init setup_earlycon_with_uartclk(char *buf, unsigned int uart_clk_freq)
{
const struct earlycon_id *match;
bool empty_compatible = true;
@@ -209,7 +216,7 @@ int __init setup_earlycon(char *buf)
} else
buf = NULL;
- return register_earlycon(buf, match);
+ return register_earlycon(buf, uart_clk_freq, match);
}
if (empty_compatible) {
diff --git a/include/linux/serial_core.h b/include/linux/serial_core.h
index 110ad4e2aef9..19d8181c9005 100644
--- a/include/linux/serial_core.h
+++ b/include/linux/serial_core.h
@@ -1097,11 +1097,18 @@ int of_setup_earlycon(const struct earlycon_id *match, unsigned long node,
#ifdef CONFIG_SERIAL_EARLYCON
extern bool earlycon_acpi_spcr_enable __initdata;
-int setup_earlycon(char *buf);
+int setup_earlycon_with_uartclk(char *buf, unsigned int uart_clk_freq);
#else
static const bool earlycon_acpi_spcr_enable EARLYCON_USED_OR_UNUSED;
-static inline int setup_earlycon(char *buf) { return 0; }
+static inline int setup_earlycon_with_uartclk(char *buf, unsigned int uart_clk_freq)
+{
+ return 0;
+}
#endif
+static inline int setup_earlycon(char *buf)
+{
+ return setup_earlycon_with_uartclk(buf, 0);
+}
/* Variant of uart_console_registered() when the console_list_lock is held. */
static inline bool uart_console_registered_locked(struct uart_port *port)
--
2.53.0
^ permalink raw reply related [flat|nested] 5+ messages in thread* [PATCH v3 2/2] ACPI: SPCR: Support UART clock frequency field
2026-06-15 0:40 [PATCH v3 0/2] ACPI: SPCR: Support UART clock frequency field Markus Probst
2026-06-15 0:40 ` [PATCH v3 1/2] serial: earlycon: add uart_clk_freq parameter Markus Probst
@ 2026-06-15 0:40 ` Markus Probst
2026-07-10 12:34 ` Greg Kroah-Hartman
1 sibling, 1 reply; 5+ messages in thread
From: Markus Probst @ 2026-06-15 0:40 UTC (permalink / raw)
To: Greg Kroah-Hartman, Jiri Slaby, Rafael J. Wysocki, Len Brown
Cc: linux-kernel, linux-serial, linux-acpi, Markus Probst
The Microsoft Serial Port Console Redirection (SPCR) specification
revision 1.08 comprises additional field: UART Clock Frequency [1].
It contains a non-zero value indicating the UART clock frequency in Hz.
Link: https://learn.microsoft.com/en-us/windows-hardware/drivers/serports/serial-port-console-redirection-table [1]
Signed-off-by: Markus Probst <markus.probst@posteo.de>
---
drivers/acpi/spcr.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/drivers/acpi/spcr.c b/drivers/acpi/spcr.c
index 73cb933fdc89..c79c809f49d4 100644
--- a/drivers/acpi/spcr.c
+++ b/drivers/acpi/spcr.c
@@ -228,7 +228,8 @@ int __init acpi_parse_spcr(bool enable_earlycon, bool enable_console)
pr_info("console: %s\n", opts);
if (enable_earlycon)
- setup_earlycon(opts);
+ setup_earlycon_with_uartclk(opts,
+ table->header.revision >= 3 ? table->uart_clk_freq : 0);
if (enable_console)
err = add_preferred_console(uart, 0, opts + strlen(uart) + 1);
--
2.53.0
^ permalink raw reply related [flat|nested] 5+ messages in thread