linux-kernel - [PATCH v1] clk: meson: change usleep_range() to udelay() for atomic context

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Date:   Mon, 3 Jul 2023 23:04:04 +0300
From:   Dmitry Rokosov <ddrokosov@...rdevices.ru>
To:     <neil.armstrong@...aro.org>, <jbrunet@...libre.com>,
        <mturquette@...libre.com>, <sboyd@...nel.org>,
        <khilman@...libre.com>, <martin.blumenstingl@...glemail.com>
CC:     <jian.hu@...ogic.com>, <kernel@...rdevices.ru>,
        <rockosov@...il.com>, <linux-amlogic@...ts.infradead.org>,
        <linux-clk@...r.kernel.org>, <devicetree@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        Dmitry Rokosov <ddrokosov@...rdevices.ru>,
        Jan Dakinevich <yvdakinevich@...rdevices.ru>
Subject: [PATCH v1] clk: meson: change usleep_range() to udelay() for atomic context

The function meson_clk_pll_enable() can be invoked under the enable_lock
spinlock from the clk core logic (please refer to
drivers/clk/clk.c:clk_core_enable_lock()), which risks a kernel panic
during the usleep_range() call:

   BUG: scheduling while atomic: kworker/u4:2/36/0x00000002
   Modules linked in: g_ffs usb_f_fs libcomposite
   CPU: 1 PID: 36 Comm: kworker/u4:2 Not tainted 6.4.0-rc5 #273
   Workqueue: events_unbound async_run_entry_fn
   Call trace:
    dump_backtrace+0x9c/0x128
    show_stack+0x20/0x38
    dump_stack_lvl+0x48/0x60
    dump_stack+0x18/0x28
    __schedule_bug+0x58/0x78
    __schedule+0x828/0xa88
    schedule+0x64/0xd8
    schedule_hrtimeout_range_clock+0xd0/0x208
    schedule_hrtimeout_range+0x1c/0x30
    usleep_range_state+0x6c/0xa8
    meson_clk_pll_enable+0x1f4/0x310
    clk_core_enable+0x78/0x200
    clk_core_enable+0x58/0x200
    clk_core_enable+0x58/0x200
    clk_core_enable+0x58/0x200
    clk_enable+0x34/0x60

Considering that this code is expected to be used in an atomic context,
it is required to use the udelay() function instead of usleep_range()
for the atomic context safety.

Fixes: b6ec400aa153 ("clk: meson: introduce new pll power-on sequence for A1 SoC family")
Reported-by: Jan Dakinevich <yvdakinevich@...rdevices.ru>
Signed-off-by: Dmitry Rokosov <ddrokosov@...rdevices.ru>
Signed-off-by: Jan Dakinevich <yvdakinevich@...rdevices.ru>
---
 drivers/clk/meson/clk-pll.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/clk/meson/clk-pll.c b/drivers/clk/meson/clk-pll.c
index 56ec2210f1ad..eef6f37c8d8d 100644
--- a/drivers/clk/meson/clk-pll.c
+++ b/drivers/clk/meson/clk-pll.c
@@ -367,9 +367,9 @@ static int meson_clk_pll_enable(struct clk_hw *hw)
 	 * 3. enable the lock detect module
 	 */
 	if (MESON_PARM_APPLICABLE(&pll->current_en)) {
-		usleep_range(10, 20);
+		udelay(10);
 		meson_parm_write(clk->map, &pll->current_en, 1);
-		usleep_range(40, 50);
+		udelay(40);
 	};
 
 	if (MESON_PARM_APPLICABLE(&pll->l_detect)) {
-- 
2.36.0