linux-kernel - [PATCH 1/2] clk: Introduce CLK_ASSUME_ENABLED_WHEN

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Message-Id: <20211203035436.3505743-1-bjorn.andersson@linaro.org>
Date:   Thu,  2 Dec 2021 19:54:35 -0800
From:   Bjorn Andersson <bjorn.andersson@...aro.org>
To:     Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        dmitry.baryshkov@...aro.org
Cc:     linux-clk@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-msm@...r.kernel.org
Subject: [PATCH 1/2] clk: Introduce CLK_ASSUME_ENABLED_WHEN_UNUSED

Some clock implementations doesn't provide means of implementing
is_enabled(), but still requires to be explicitly disabled when found
unused as part of clk_disable_unused().

One such set of clocks are Qualcomm's display RCGs. These can be enabled
and disabled automatically by the hardware, so it's not possible to
reliably query their configuration. Further more, these clocks need to
be disabled when unused, to allow them to be "parked" onto a safe
parent. Failure to disable the RCG results in the hardware locking up as
clk_disable_unused() traverses up the tree and turns off its source
clocks.

Add a new flag, CLK_ASSUME_ENABLED_BOOT, which clock drivers can use to
signal that these clocks should be disabled even if they don't implement
the is_enabled() ops.

Signed-off-by: Bjorn Andersson <bjorn.andersson@...aro.org>
---
 drivers/clk/clk.c            | 2 +-
 include/linux/clk-provider.h | 2 ++
 2 files changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
index f467d63bbf1e..e0bb53cbd4c8 100644
--- a/drivers/clk/clk.c
+++ b/drivers/clk/clk.c
@@ -1265,7 +1265,7 @@ static void __init clk_disable_unused_subtree(struct clk_core *core)
 	 * sequence.  call .disable_unused if available, otherwise fall
 	 * back to .disable
 	 */
-	if (clk_core_is_enabled(core)) {
+	if (clk_core_is_enabled(core) || core->flags & CLK_ASSUME_ENABLED_WHEN_UNUSED) {
 		trace_clk_disable(core);
 		if (core->ops->disable_unused)
 			core->ops->disable_unused(core->hw);
diff --git a/include/linux/clk-provider.h b/include/linux/clk-provider.h
index f59c875271a0..7661cce31fa1 100644
--- a/include/linux/clk-provider.h
+++ b/include/linux/clk-provider.h
@@ -32,6 +32,8 @@
 #define CLK_OPS_PARENT_ENABLE	BIT(12)
 /* duty cycle call may be forwarded to the parent clock */
 #define CLK_DUTY_CYCLE_PARENT	BIT(13)
+/* assume clock is enabled if found unused in late init */
+#define CLK_ASSUME_ENABLED_WHEN_UNUSED	BIT(14)

 struct clk;
 struct clk_hw;
-- 
2.33.1