linux-kernel - [RFC] clk: Mark HW enabled clocks as enabled in core

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Message-Id: <1611660096-12381-1-git-send-email-abel.vesa@nxp.com>
Date:   Tue, 26 Jan 2021 13:21:36 +0200
From:   Abel Vesa <abel.vesa@....com>
To:     Mike Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>,
        Sascha Hauer <kernel@...gutronix.de>,
        Lucas Stach <l.stach@...gutronix.de>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-clk@...r.kernel.org, Abel Vesa <abel.vesa@....com>
Subject: [RFC] clk: Mark HW enabled clocks as enabled in core

Some clocks are already enabled in HW even before the kernel
starts to boot. So, in order to make sure that these clocks do not
get disabled when clk_disable_unused call is done or when
reparenting clocks, we enable them in core on clock registration.
Such a clock will have to be registered with CLK_IGNORE_UNUSED flag
and also needs to have the is_enabled ops implemented.

Signed-off-by: Abel Vesa <abel.vesa@....com>
---
 drivers/clk/clk.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
index 3d751ae5bc70..26d55851cfa5 100644
--- a/drivers/clk/clk.c
+++ b/drivers/clk/clk.c
@@ -3416,6 +3416,7 @@ static int __clk_core_init(struct clk_core *core)
 	int ret;
 	struct clk_core *parent;
 	unsigned long rate;
+	bool is_hw_enabled = false;
 	int phase;
 
 	if (!core)
@@ -3558,12 +3559,20 @@ static int __clk_core_init(struct clk_core *core)
 		rate = 0;
 	core->rate = core->req_rate = rate;
 
+	/*
+	 * If the clock has the CLK_IGNORE_UNUSED flag set and it is already
+	 * enabled in HW, enable it in core too so it won't get accidentally
+	 * disabled when walking the orphan tree and reparenting clocks
+	 */
+	if (core->flags & CLK_IGNORE_UNUSED && core->ops->is_enabled)
+		is_hw_enabled = clk_core_is_enabled(core);
+
 	/*
 	 * Enable CLK_IS_CRITICAL clocks so newly added critical clocks
 	 * don't get accidentally disabled when walking the orphan tree and
 	 * reparenting clocks
 	 */
-	if (core->flags & CLK_IS_CRITICAL) {
+	if (core->flags & CLK_IS_CRITICAL || is_hw_enabled) {
 		unsigned long flags;
 
 		ret = clk_core_prepare(core);
-- 
2.29.2