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[PATCH] pwm: meson: handle unknown ID values

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  [PATCH] pwm: meson: handle unknown ID values Arnd Bergmann <arnd@arndb.de> - 2016-09-06 15:00 +0200
    Re: [PATCH] pwm: meson: handle unknown ID values Thierry Reding <thierry.reding@gmail.com> - 2016-09-08 11:30 +0200
      Re: [PATCH] pwm: meson: handle unknown ID values Arnd Bergmann <arnd@arndb.de> - 2016-09-08 11:40 +0200

#1477343 — [PATCH] pwm: meson: handle unknown ID values

When building with -Wmaybe-uninitialized, we get a couple of harmless
warnings about three functions in this new driver that don't look
safe to the compiler:

drivers/pwm/pwm-meson.c: In function 'meson_pwm_get_state':
drivers/pwm/pwm-meson.c:355:26: error: 'mask' may be used uninitialized in this function [-Werror=maybe-uninitialized]
drivers/pwm/pwm-meson.c: In function 'meson_pwm_disable':
drivers/pwm/pwm-meson.c:263:13: error: 'enable' may be used uninitialized in this function [-Werror=maybe-uninitialized]
drivers/pwm/pwm-meson.c: In function 'meson_pwm_apply':
drivers/pwm/pwm-meson.c:231:13: error: 'clk_shift' may be used uninitialized in this function [-Werror=maybe-uninitialized]
drivers/pwm/pwm-meson.c:231:36: error: 'enable' may be used uninitialized in this function [-Werror=maybe-uninitialized]
drivers/pwm/pwm-meson.c:231:24: error: 'clk_enable' may be used uninitialized in this function [-Werror=maybe-uninitialized]

Specifically, if we have a device with an id other than 0 or 1,
this would result in undefined behavior. This is currently not
possible, but the compiler cannot be expected to know this.

This patch adds a 'default' clause to let the compiler know
what to do instead, which shuts up the warning and makes the
code slightly more resiliant in case it gets extended to other
identifiers.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
 drivers/pwm/pwm-meson.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/drivers/pwm/pwm-meson.c b/drivers/pwm/pwm-meson.c
index 566f5cb81021..25abd95dcc7b 100644
--- a/drivers/pwm/pwm-meson.c
+++ b/drivers/pwm/pwm-meson.c
@@ -242,6 +242,9 @@ static void meson_pwm_enable(struct meson_pwm *meson,
 		clk_enable = MISC_B_CLK_EN;
 		enable = MISC_B_EN;
 		break;
+
+	default:
+		return;
 	}
 
 	value = readl(meson->base + REG_MISC_AB);
@@ -270,6 +273,9 @@ static void meson_pwm_disable(struct meson_pwm *meson, unsigned int id)
 	case 1:
 		enable = MISC_B_EN;
 		break;
+
+	default:
+		return;
 	}
 
 	value = readl(meson->base + REG_MISC_AB);
@@ -349,6 +355,10 @@ static void meson_pwm_get_state(struct pwm_chip *chip, struct pwm_device *pwm,
 	case 1:
 		mask = MISC_B_EN;
 		break;
+
+	default:
+		state->enabled = 0;
+		return;
 	}
 
 	value = readl(meson->base + REG_MISC_AB);
-- 
2.9.0

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#1478968

[Multipart message — attachments visible in raw view] — view raw

On Tue, Sep 06, 2016 at 02:50:47PM +0200, Arnd Bergmann wrote:
> When building with -Wmaybe-uninitialized, we get a couple of harmless
> warnings about three functions in this new driver that don't look
> safe to the compiler:
> 
> drivers/pwm/pwm-meson.c: In function 'meson_pwm_get_state':
> drivers/pwm/pwm-meson.c:355:26: error: 'mask' may be used uninitialized in this function [-Werror=maybe-uninitialized]
> drivers/pwm/pwm-meson.c: In function 'meson_pwm_disable':
> drivers/pwm/pwm-meson.c:263:13: error: 'enable' may be used uninitialized in this function [-Werror=maybe-uninitialized]
> drivers/pwm/pwm-meson.c: In function 'meson_pwm_apply':
> drivers/pwm/pwm-meson.c:231:13: error: 'clk_shift' may be used uninitialized in this function [-Werror=maybe-uninitialized]
> drivers/pwm/pwm-meson.c:231:36: error: 'enable' may be used uninitialized in this function [-Werror=maybe-uninitialized]
> drivers/pwm/pwm-meson.c:231:24: error: 'clk_enable' may be used uninitialized in this function [-Werror=maybe-uninitialized]
> 
> Specifically, if we have a device with an id other than 0 or 1,
> this would result in undefined behavior. This is currently not
> possible, but the compiler cannot be expected to know this.
> 
> This patch adds a 'default' clause to let the compiler know
> what to do instead, which shuts up the warning and makes the
> code slightly more resiliant in case it gets extended to other
> identifiers.
> 
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> ---
>  drivers/pwm/pwm-meson.c | 10 ++++++++++
>  1 file changed, 10 insertions(+)

Applied, though I left out the dummy assignment of state->enabled = 0
because that's dead code anyway.

Thanks,
Thierry

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#1478973

On Thursday, September 8, 2016 11:23:54 AM CEST Thierry Reding wrote:
> On Tue, Sep 06, 2016 at 02:50:47PM +0200, Arnd Bergmann wrote:
> > When building with -Wmaybe-uninitialized, we get a couple of harmless
> > warnings about three functions in this new driver that don't look
> > safe to the compiler:
> > 
> > drivers/pwm/pwm-meson.c: In function 'meson_pwm_get_state':
> > drivers/pwm/pwm-meson.c:355:26: error: 'mask' may be used uninitialized in this function [-Werror=maybe-uninitialized]
> > drivers/pwm/pwm-meson.c: In function 'meson_pwm_disable':
> > drivers/pwm/pwm-meson.c:263:13: error: 'enable' may be used uninitialized in this function [-Werror=maybe-uninitialized]
> > drivers/pwm/pwm-meson.c: In function 'meson_pwm_apply':
> > drivers/pwm/pwm-meson.c:231:13: error: 'clk_shift' may be used uninitialized in this function [-Werror=maybe-uninitialized]
> > drivers/pwm/pwm-meson.c:231:36: error: 'enable' may be used uninitialized in this function [-Werror=maybe-uninitialized]
> > drivers/pwm/pwm-meson.c:231:24: error: 'clk_enable' may be used uninitialized in this function [-Werror=maybe-uninitialized]
> > 
> > Specifically, if we have a device with an id other than 0 or 1,
> > this would result in undefined behavior. This is currently not
> > possible, but the compiler cannot be expected to know this.
> > 
> > This patch adds a 'default' clause to let the compiler know
> > what to do instead, which shuts up the warning and makes the
> > code slightly more resiliant in case it gets extended to other
> > identifiers.
> > 
> > Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> > ---
> >  drivers/pwm/pwm-meson.c | 10 ++++++++++
> >  1 file changed, 10 insertions(+)
> 
> Applied, though I left out the dummy assignment of state->enabled = 0
> because that's dead code anyway.

Sounds good. My first version had "break" instead of "return" there,
so it required the assignment,  but you are in the current version you
are right that we are better off without it.

	Arnd

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