From: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
To: thierry.reding@gmail.com, narmstrong@baylibre.com,
jbrunet@baylibre.com, linux-pwm@vger.kernel.org,
linux-amlogic@lists.infradead.org
Cc: linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org,
Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Subject: [PATCH 1/1] pwm: meson: use the spin-lock only to protect register modifications
Date: Sun, 24 Mar 2019 23:02:17 +0100 [thread overview]
Message-ID: <20190324220217.15813-2-martin.blumenstingl@googlemail.com> (raw)
In-Reply-To: <20190324220217.15813-1-martin.blumenstingl@googlemail.com>
Holding the spin-lock for all of the code in meson_pwm_apply() can
result in a "BUG: scheduling while atomic". This can happen because
clk_get_rate() (which is called from meson_pwm_calc()) may sleep.
Only hold the spin-lock when modifying registers to solve this.
The reason why we need a spin-lock in the driver is because the
REG_MISC_AB register is shared between the two channels provided by one
PWM controller. The only functions where REG_MISC_AB is modified are
meson_pwm_enable() and meson_pwm_disable() so the register reads/writes
in there need to be protected by the spin-lock.
The original code also used the spin-lock to protect the values in
struct meson_pwm_channel. This could be necessary if two consumers can
use the same PWM channel. However, PWM core doesn't allow this so we
don't need to protect the values in struct meson_pwm_channel with a
lock.
Fixes: 211ed630753d2f ("pwm: Add support for Meson PWM Controller")
Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
---
drivers/pwm/pwm-meson.c | 21 +++++++++++++--------
1 file changed, 13 insertions(+), 8 deletions(-)
diff --git a/drivers/pwm/pwm-meson.c b/drivers/pwm/pwm-meson.c
index c1ed641b3e26..2b03938039b6 100644
--- a/drivers/pwm/pwm-meson.c
+++ b/drivers/pwm/pwm-meson.c
@@ -235,6 +235,7 @@ static void meson_pwm_enable(struct meson_pwm *meson,
{
u32 value, clk_shift, clk_enable, enable;
unsigned int offset;
+ unsigned long flags;
switch (id) {
case 0:
@@ -255,6 +256,8 @@ static void meson_pwm_enable(struct meson_pwm *meson,
return;
}
+ spin_lock_irqsave(&meson->lock, flags);
+
value = readl(meson->base + REG_MISC_AB);
value &= ~(MISC_CLK_DIV_MASK << clk_shift);
value |= channel->pre_div << clk_shift;
@@ -267,11 +270,14 @@ static void meson_pwm_enable(struct meson_pwm *meson,
value = readl(meson->base + REG_MISC_AB);
value |= enable;
writel(value, meson->base + REG_MISC_AB);
+
+ spin_unlock_irqrestore(&meson->lock, flags);
}
static void meson_pwm_disable(struct meson_pwm *meson, unsigned int id)
{
u32 value, enable;
+ unsigned long flags;
switch (id) {
case 0:
@@ -286,9 +292,13 @@ static void meson_pwm_disable(struct meson_pwm *meson, unsigned int id)
return;
}
+ spin_lock_irqsave(&meson->lock, flags);
+
value = readl(meson->base + REG_MISC_AB);
value &= ~enable;
writel(value, meson->base + REG_MISC_AB);
+
+ spin_unlock_irqrestore(&meson->lock, flags);
}
static int meson_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm,
@@ -296,19 +306,16 @@ static int meson_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm,
{
struct meson_pwm_channel *channel = pwm_get_chip_data(pwm);
struct meson_pwm *meson = to_meson_pwm(chip);
- unsigned long flags;
int err = 0;
if (!state)
return -EINVAL;
- spin_lock_irqsave(&meson->lock, flags);
-
if (!state->enabled) {
meson_pwm_disable(meson, pwm->hwpwm);
channel->state.enabled = false;
- goto unlock;
+ return 0;
}
if (state->period != channel->state.period ||
@@ -329,7 +336,7 @@ static int meson_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm,
err = meson_pwm_calc(meson, channel, pwm->hwpwm,
state->duty_cycle, state->period);
if (err < 0)
- goto unlock;
+ return err;
channel->state.polarity = state->polarity;
channel->state.period = state->period;
@@ -341,9 +348,7 @@ static int meson_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm,
channel->state.enabled = true;
}
-unlock:
- spin_unlock_irqrestore(&meson->lock, flags);
- return err;
+ return 0;
}
static void meson_pwm_get_state(struct pwm_chip *chip, struct pwm_device *pwm,
--
2.21.0
next prev parent reply other threads:[~2019-03-24 22:02 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-03-24 22:02 [PATCH 0/1] pwm: meson: fix scheduling while atomic issue Martin Blumenstingl
2019-03-24 22:02 ` Martin Blumenstingl [this message]
2019-03-25 8:48 ` [PATCH 1/1] pwm: meson: use the spin-lock only to protect register modifications Uwe Kleine-König
2019-03-25 8:41 ` [PATCH 0/1] pwm: meson: fix scheduling while atomic issue Uwe Kleine-König
2019-03-25 8:50 ` Uwe Kleine-König
2019-03-25 17:41 ` Martin Blumenstingl
2019-03-25 20:07 ` Uwe Kleine-König
2019-03-26 20:05 ` Martin Blumenstingl
2019-03-30 19:29 ` Martin Blumenstingl
2019-03-31 18:47 ` Uwe Kleine-König
2019-04-01 7:25 ` Neil Armstrong
2019-03-26 9:06 ` Neil Armstrong
2019-03-26 10:54 ` Uwe Kleine-König
2019-03-25 9:35 ` Jerome Brunet
2019-03-25 18:04 ` Martin Blumenstingl
2019-03-26 8:37 ` Jerome Brunet
2019-03-26 8:57 ` Neil Armstrong
2019-03-26 20:16 ` Martin Blumenstingl
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20190324220217.15813-2-martin.blumenstingl@googlemail.com \
--to=martin.blumenstingl@googlemail.com \
--cc=jbrunet@baylibre.com \
--cc=linux-amlogic@lists.infradead.org \
--cc=linux-arm-kernel@lists.infradead.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-pwm@vger.kernel.org \
--cc=narmstrong@baylibre.com \
--cc=thierry.reding@gmail.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).