[PATCH 2/4] serial: amba-pl011: Introduce set_uartclk_rate vendor flag

Kartik Rajput
2026-02-25T06:59:47Z

The NVIDIA Tegra264 UART relies on configuring the UART clock rate
directly to program the desired baud rate.

Introduce the set_uartclk_rate vendor flag. When set, the driver
uses clk_set_rate() to program the UART clock to the desired baud
rate and clk_round_rate() to determine the maximum supported baud
rate.

Signed-off-by: Kartik Rajput <kkartik@nvidia.com>
---
drivers/tty/serial/amba-pl011.c | 29 +++++++++++++++++++++++++++--
1 file changed, 27 insertions(+), 2 deletions(-)

diff --git a/drivers/tty/serial/amba-pl011.c b/drivers/tty/serial/amba-pl011.c
index 79e1c937a600..ad06dc4cdf6e 100644
--- a/drivers/tty/serial/amba-pl011.c
+++ b/drivers/tty/serial/amba-pl011.c
@@ -115,6 +115,7 @@ struct vendor_data {
bool always_enabled;
bool fixed_options;
bool skip_ibrd_fbrd;
+ bool set_uartclk_rate;

unsigned int (*get_fifosize)(struct amba_device *dev);
};
@@ -2096,6 +2097,7 @@ pl011_set_termios(struct uart_port *port, struct ktermios *termios,
unsigned int lcr_h, old_cr;
unsigned long flags;
unsigned int baud, quot, clkdiv;
+ unsigned int max_baud;
unsigned int bits;

if (uap->vendor->oversampling)
@@ -2103,11 +2105,34 @@ pl011_set_termios(struct uart_port *port, struct ktermios *termios,
else
clkdiv = 16;

+ max_baud = port->uartclk / clkdiv;
+
+ if (uap->vendor->set_uartclk_rate) {
+ long max_clkrate = clk_round_rate(uap->clk, UINT_MAX);
+
+ /*
+ * Clock is reprogrammable - determine max baud from the clock's
+ * maximum rate, not the current uartclk.
+ */
+ if (max_clkrate > 0)
+ max_baud = max_clkrate / clkdiv;
+ }
+
/*
* Ask the core to calculate the divisor for us.
*/
- baud = uart_get_baud_rate(port, termios, old, 0,
- port->uartclk / clkdiv);
+ baud = uart_get_baud_rate(port, termios, old, 0, max_baud);
+
+ if (uap->vendor->set_uartclk_rate) {
+ int err;
+
+ err = clk_set_rate(uap->clk, baud * clkdiv);
+ if (err) {
+ dev_err(port->dev, "Failed to set clock rate: %d\n", err);
+ return;
+ }
+ }
+
#ifdef CONFIG_DMA_ENGINE
/*
* Adjust RX DMA polling rate with baud rate if not specified.
--
2.43.0