linux-kernel - [PATCH v3 2/3] serial: 8250_of: add support for an optional bus clock

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Message-ID: <20250411154419.1379529-3-elder@riscstar.com>
Date: Fri, 11 Apr 2025 10:44:17 -0500
From: Alex Elder <elder@...cstar.com>
To: gregkh@...uxfoundation.org,
	jirislaby@...nel.org,
	robh@...nel.org,
	krzk+dt@...nel.org,
	conor+dt@...nel.org
Cc: dlan@...too.org,
	benjamin.larsson@...exis.eu,
	bastien.curutchet@...tlin.com,
	andriy.shevchenko@...ux.intel.com,
	u.kleine-koenig@...libre.com,
	lkundrak@...sk,
	devicetree@...r.kernel.org,
	linux-serial@...r.kernel.org,
	spacemit@...ts.linux.dev,
	linux-kernel@...r.kernel.org
Subject: [PATCH v3 2/3] serial: 8250_of: add support for an optional bus clock

The SpacemiT UART requires a bus clock to be enabled, in addition to
it's "normal" core clock.  Look up the optional bus clock by name,
and if that's found, look up the core clock using the name "core".

Supplying a bus clock is optional.  If no bus clock is needed, the
the first/only clock is used for the core clock.

Signed-off-by: Alex Elder <elder@...cstar.com>
---
 drivers/tty/serial/8250/8250_of.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/drivers/tty/serial/8250/8250_of.c b/drivers/tty/serial/8250/8250_of.c
index 11c860ea80f60..a90a5462aa72a 100644
--- a/drivers/tty/serial/8250/8250_of.c
+++ b/drivers/tty/serial/8250/8250_of.c
@@ -123,7 +123,16 @@ static int of_platform_serial_setup(struct platform_device *ofdev,
 
 	/* Get clk rate through clk driver if present */
 	if (!port->uartclk) {
-		info->clk = devm_clk_get_enabled(dev, NULL);
+		struct clk *bus_clk;
+
+		bus_clk = devm_clk_get_optional_enabled(dev, "bus");
+		if (IS_ERR(bus_clk)) {
+			ret = dev_err_probe(dev, PTR_ERR(bus_clk), "failed to get bus clock\n");
+			goto err_pmruntime;
+		}
+
+		/* If the bus clock is required, core clock must be named */
+		info->clk = devm_clk_get_enabled(dev, bus_clk ? "core" : NULL);
 		if (IS_ERR(info->clk)) {
 			ret = dev_err_probe(dev, PTR_ERR(info->clk), "failed to get clock\n");
 			goto err_pmruntime;
-- 
2.45.2