linux-kernel - [PATCH 5.4 101/168] tty: serial: owl: add "much needed" clk_prepare

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Date:   Tue, 28 Apr 2020 20:24:35 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Amit Singh Tomar <amittomer25@...il.com>
Subject: [PATCH 5.4 101/168] tty: serial: owl: add "much needed" clk_prepare_enable()

From: Amit Singh Tomar <amittomer25@...il.com>

commit abf42d2f333b21bf8d33b2fbb8a85fa62037ac01 upstream.

commit 8ba92cf59335 ("arm64: dts: actions: s700: Add Clock Management Unit")
breaks the UART on Cubieboard7-lite (based on S700 SoC), This is due to the
fact that generic clk routine clk_disable_unused() disables the gate clks,
and that in turns disables OWL UART (but UART driver never enables it). To
prove this theory, Andre suggested to use "clk_ignore_unused" in kernel
commnd line and it worked (Kernel happily lands into RAMFS world :)).

This commit fix this up by adding clk_prepare_enable().

Fixes: 8ba92cf59335 ("arm64: dts: actions: s700: Add Clock Management Unit")
Signed-off-by: Amit Singh Tomar <amittomer25@...il.com>
Cc: stable <stable@...r.kernel.org>
Link: https://lore.kernel.org/r/1587067917-1400-1-git-send-email-amittomer25@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 drivers/tty/serial/owl-uart.c |    7 +++++++
 1 file changed, 7 insertions(+)

--- a/drivers/tty/serial/owl-uart.c
+++ b/drivers/tty/serial/owl-uart.c
@@ -680,6 +680,12 @@ static int owl_uart_probe(struct platfor
 		return PTR_ERR(owl_port->clk);
 	}
 
+	ret = clk_prepare_enable(owl_port->clk);
+	if (ret) {
+		dev_err(&pdev->dev, "could not enable clk\n");
+		return ret;
+	}
+
 	owl_port->port.dev = &pdev->dev;
 	owl_port->port.line = pdev->id;
 	owl_port->port.type = PORT_OWL;
@@ -712,6 +718,7 @@ static int owl_uart_remove(struct platfo
 
 	uart_remove_one_port(&owl_uart_driver, &owl_port->port);
 	owl_uart_ports[pdev->id] = NULL;
+	clk_disable_unprepare(owl_port->clk);
 
 	return 0;
 }