linux-kernel - [PATCH v3] clk: expand clk_ignore_unused mechanism to keep only a few clks on

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Date:   Wed, 26 Oct 2022 17:18:12 +0200
From:   Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>
To:     Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>
Cc:     linux-doc@...r.kernel.org, linux-clk@...r.kernel.org,
        linux-kernel@...r.kernel.org, kernel@...gutronix.de,
        Jonathan Corbet <corbet@....net>
Subject: [PATCH v3] clk: expand clk_ignore_unused mechanism to keep only a few clks on

Allow to pass an integer n that results in only keeping n unused clocks
enabled.

This helps to debug the problem if you only know that clk_ignore_unused
helps but you have no clue yet which clock is the culprit.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
---
Hello,

compared to v2 sent in August 2021 this is a trivial rebase on top of
v6.1-rc1. I pinged that one repeatedly, I'm now trying with resending
and calling the rebased patch v3 to maybe get some feedback. :-\

Best regards
Uwe

 Documentation/driver-api/clk.rst |  4 +++-
 drivers/clk/clk.c                | 33 ++++++++++++++++++++++++--------
 2 files changed, 28 insertions(+), 9 deletions(-)

diff --git a/Documentation/driver-api/clk.rst b/Documentation/driver-api/clk.rst
index 3cad45d14187..65ae7c3e2b33 100644
--- a/Documentation/driver-api/clk.rst
+++ b/Documentation/driver-api/clk.rst
@@ -259,7 +259,9 @@ the disabling means that the driver will remain functional while the issues
 are sorted out.
 
 To bypass this disabling, include "clk_ignore_unused" in the bootargs to the
-kernel.
+kernel. If you pass "clk_ignore_unused=n" (where n is an integer) the first n
+found clocks are not disabled which can be useful for bisecting over the unused
+clks if you don't know yet which of them is reponsible for your problem.
 
 Locking
 =======
diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
index c3c3f8c07258..356119a7e5fe 100644
--- a/drivers/clk/clk.c
+++ b/drivers/clk/clk.c
@@ -1322,6 +1322,8 @@ static void __init clk_unprepare_unused_subtree(struct clk_core *core)
 	clk_pm_runtime_put(core);
 }
 
+static unsigned clk_unused_keep_on __initdata;
+
 static void __init clk_disable_unused_subtree(struct clk_core *core)
 {
 	struct clk_core *child;
@@ -1352,12 +1354,17 @@ static void __init clk_disable_unused_subtree(struct clk_core *core)
 	 * back to .disable
 	 */
 	if (clk_core_is_enabled(core)) {
-		trace_clk_disable(core);
-		if (core->ops->disable_unused)
-			core->ops->disable_unused(core->hw);
-		else if (core->ops->disable)
-			core->ops->disable(core->hw);
-		trace_clk_disable_complete(core);
+		if (clk_unused_keep_on) {
+			pr_warn("Keep unused clk \"%s\" on\n", core->name);
+			clk_unused_keep_on -= 1;
+		} else {
+			trace_clk_disable(core);
+			if (core->ops->disable_unused)
+				core->ops->disable_unused(core->hw);
+			else if (core->ops->disable)
+				core->ops->disable(core->hw);
+			trace_clk_disable_complete(core);
+		}
 	}
 
 unlock_out:
@@ -1369,9 +1376,17 @@ static void __init clk_disable_unused_subtree(struct clk_core *core)
 }
 
 static bool clk_ignore_unused __initdata;
-static int __init clk_ignore_unused_setup(char *__unused)
+static int __init clk_ignore_unused_setup(char *keep)
 {
-	clk_ignore_unused = true;
+	if (*keep == '=') {
+		int ret;
+
+		ret = kstrtouint(keep + 1, 0, &clk_unused_keep_on);
+		if (ret < 0)
+			pr_err("Warning: failed to parse clk_ignore_unused parameter, ignoring");
+	} else {
+		clk_ignore_unused = true;
+	}
 	return 1;
 }
 __setup("clk_ignore_unused", clk_ignore_unused_setup);
@@ -1383,6 +1398,8 @@ static int __init clk_disable_unused(void)
 	if (clk_ignore_unused) {
 		pr_warn("clk: Not disabling unused clocks\n");
 		return 0;
+	} else if (clk_unused_keep_on) {
+		pr_warn("clk: Not disabling %u unused clocks\n", clk_unused_keep_on);
 	}
 
 	clk_prepare_lock();
-- 
2.37.2