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

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Message-ID: <20250408175146.979557-3-elder@riscstar.com>
Date: Tue,  8 Apr 2025 12:51:43 -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: 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,
	linux-kernel@...r.kernel.org
Subject: [PATCH 2/2] 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 core clock by name, and if
that's found, look up the bus clock.  If named clocks are used, both
are required.

Supplying a bus clock is optional.  If no bus clock is needed, the clocks
aren't named and we only look up the first clock.

Signed-off-by: Alex Elder <elder@...cstar.com>
---
 drivers/tty/serial/8250/8250_of.c | 25 +++++++++++++++++++++++--
 1 file changed, 23 insertions(+), 2 deletions(-)

diff --git a/drivers/tty/serial/8250/8250_of.c b/drivers/tty/serial/8250/8250_of.c
index 11c860ea80f60..0ffb9f2727b92 100644
--- a/drivers/tty/serial/8250/8250_of.c
+++ b/drivers/tty/serial/8250/8250_of.c
@@ -24,6 +24,7 @@
 
 struct of_serial_info {
 	struct clk *clk;
+	struct clk *bus_clk;
 	struct reset_control *rst;
 	int type;
 	int line;
@@ -123,14 +124,34 @@ 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);
+		info->clk = devm_clk_get_optional_enabled(dev, "core");
 		if (IS_ERR(info->clk)) {
-			ret = dev_err_probe(dev, PTR_ERR(info->clk), "failed to get clock\n");
+			ret = dev_err_probe(dev, PTR_ERR(info->clk),
+					    "failed to get core clock\n");
 			goto err_pmruntime;
 		}
 
+		/* If we got the core clock, look for a bus clock */
+		if (info->clk) {
+			info->bus_clk = devm_clk_get_enabled(dev, "bus");
+			if (IS_ERR(info->bus_clk)) {
+				ret = dev_err_probe(dev, PTR_ERR(info->bus_clk),
+					    "failed to get bus clock\n");
+				goto err_pmruntime;
+			}
+		} else {
+			/* Fall back to getting the one unnamed clock */
+			info->clk = devm_clk_get_enabled(dev, NULL);
+			if (IS_ERR(info->clk)) {
+				ret = dev_err_probe(dev, PTR_ERR(info->clk),
+						"failed to get clock\n");
+				goto err_pmruntime;
+			}
+		}
+
 		port->uartclk = clk_get_rate(info->clk);
 	}
+
 	/* If current-speed was set, then try not to change it. */
 	if (of_property_read_u32(np, "current-speed", &spd) == 0)
 		port->custom_divisor = port->uartclk / (16 * spd);
-- 
2.45.2