linux-kernel - [PATCH v3 1/2] clk: use ULONG_MAX as the initial value for the iteration in clk_mux_determine_rate

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <20230421-clk-v3-1-9ff79e7e7fed@outlook.com>
Date:   Thu, 27 Apr 2023 03:34:16 +0800
From:   Yang Xiwen via B4 Relay 
        <devnull+forbidden405.outlook.com@...nel.org>
To:     Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>
Cc:     linux-clk@...r.kernel.org, linux-kernel@...r.kernel.org,
        Yang Xiwen <forbidden405@...look.com>
Subject: [PATCH v3 1/2] clk: use ULONG_MAX as the initial value for the
 iteration in clk_mux_determine_rate_flags()

From: Yang Xiwen <forbidden405@...look.com>

Currently, clk_mux_determine_rate_flags() use 0 as the initial value for
selecting the best matching parent. However, this will choose a
non-existant rate(0) if the requested rate is closer to 0 than the
minimum rate the parents have.

Fix that by initializing the initial value to ULONG_MAX and treat it as a
magic number.

Signed-off-by: Yang Xiwen <forbidden405@...look.com>
---
 drivers/clk/clk.c | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
index ae07685c7588b..6184d4aa88193 100644
--- a/drivers/clk/clk.c
+++ b/drivers/clk/clk.c
@@ -541,6 +541,17 @@ EXPORT_SYMBOL_GPL(__clk_is_enabled);
 static bool mux_is_better_rate(unsigned long rate, unsigned long now,
 			   unsigned long best, unsigned long flags)
 {
+	if (rate == ULONG_MAX) {
+		// select the highest clock rate
+		if (best == ULONG_MAX)
+			return true;
+		else
+			return now > best;
+	}
+
+	if (best == ULONG_MAX && now <= rate)
+		return true;
+
 	if (flags & CLK_MUX_ROUND_CLOSEST)
 		return abs(now - rate) < abs(best - rate);
 
@@ -600,7 +611,7 @@ int clk_mux_determine_rate_flags(struct clk_hw *hw,
 {
 	struct clk_core *core = hw->core, *parent, *best_parent = NULL;
 	int i, num_parents, ret;
-	unsigned long best = 0;
+	unsigned long best = ULONG_MAX;
 
 	/* if NO_REPARENT flag set, pass through to current parent */
 	if (core->flags & CLK_SET_RATE_NO_REPARENT) {

-- 
2.39.2