[PATCH] da9052: ensure da9052_ts_input_open will not lock up on irq flood

[PATCH] da9052: ensure da9052_ts_input_open will not lock up on irq flood

[Michael Grzeschik]

It is possible that da9052_ts_input_open is called and the touchscreen
is triggering continuous interrupts. In this case we will never leave
da9052_ts_input_open. The da9052_reg_update will never get the i2c bus
as the interrupt handler will continuously lock it.

This patch switch places of da9052_reg_update and the setting of
tsi->stopped. This way its ensured that da9052_ts_input_open will never
lockup on interrupt flood.

Signed-off-by: Michael Grzeschik <m.grzeschik@pengutronix.de>
---
 drivers/input/touchscreen/da9052_tsi.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/drivers/input/touchscreen/da9052_tsi.c b/drivers/input/touchscreen/da9052_tsi.c
index 5a013bb..1b136b8 100644
--- a/drivers/input/touchscreen/da9052_tsi.c
+++ b/drivers/input/touchscreen/da9052_tsi.c
@@ -189,17 +189,20 @@ static int da9052_configure_tsi(struct da9052_tsi *tsi)
 
 static int da9052_ts_input_open(struct input_dev *input_dev)
 {
+	int val;
 	struct da9052_tsi *tsi = input_get_drvdata(input_dev);
 
-	tsi->stopped = false;
-	mb();
+	val = da9052_reg_update(tsi->da9052, DA9052_TSI_CONT_A_REG,
+				 1 << 1, 1 << 1);
 
 	/* Unmask PEN_DOWN event */
 	da9052_enable_irq(tsi->da9052, DA9052_IRQ_PENDOWN);
 
+	tsi->stopped = false;
+	mb();
+
 	/* Enable Pen Detect Circuit */
-	return da9052_reg_update(tsi->da9052, DA9052_TSI_CONT_A_REG,
-				 1 << 1, 1 << 1);
+	return val;
 }
 
 static void da9052_ts_input_close(struct input_dev *input_dev)
-- 
2.7.0

Re: [PATCH] da9052: ensure da9052_ts_input_open will not lock up on irq flood

[Dmitry Torokhov]

On Thu, Mar 03, 2016 at 11:52:02AM +0100, Michael Grzeschik wrote:
> It is possible that da9052_ts_input_open is called and the touchscreen
> is triggering continuous interrupts. In this case we will never leave
> da9052_ts_input_open. The da9052_reg_update will never get the i2c bus
> as the interrupt handler will continuously lock it.
> 
> This patch switch places of da9052_reg_update and the setting of
> tsi->stopped. This way its ensured that da9052_ts_input_open will never
> lockup on interrupt flood.

I understand what you are saying about updating register, however I do
not understand why we would want to swap unmasking pendown event ans
clearing the "stopped" flag.

Thanks.

> 
> Signed-off-by: Michael Grzeschik <m.grzeschik@pengutronix.de>
> ---
>  drivers/input/touchscreen/da9052_tsi.c | 11 +++++++----
>  1 file changed, 7 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/input/touchscreen/da9052_tsi.c b/drivers/input/touchscreen/da9052_tsi.c
> index 5a013bb..1b136b8 100644
> --- a/drivers/input/touchscreen/da9052_tsi.c
> +++ b/drivers/input/touchscreen/da9052_tsi.c
> @@ -189,17 +189,20 @@ static int da9052_configure_tsi(struct da9052_tsi *tsi)
>  
>  static int da9052_ts_input_open(struct input_dev *input_dev)
>  {
> +	int val;
>  	struct da9052_tsi *tsi = input_get_drvdata(input_dev);
>  
> -	tsi->stopped = false;
> -	mb();
> +	val = da9052_reg_update(tsi->da9052, DA9052_TSI_CONT_A_REG,
> +				 1 << 1, 1 << 1);
>  
>  	/* Unmask PEN_DOWN event */
>  	da9052_enable_irq(tsi->da9052, DA9052_IRQ_PENDOWN);
>  
> +	tsi->stopped = false;
> +	mb();
> +
>  	/* Enable Pen Detect Circuit */
> -	return da9052_reg_update(tsi->da9052, DA9052_TSI_CONT_A_REG,
> -				 1 << 1, 1 << 1);
> +	return val;
>  }
>  
>  static void da9052_ts_input_close(struct input_dev *input_dev)
> -- 
> 2.7.0
> 

-- 
Dmitry

Re: [PATCH] da9052: ensure da9052_ts_input_open will not lock up on irq flood

[Michael Grzeschik]

On Fri, Mar 11, 2016 at 11:33:11AM -0800, Dmitry Torokhov wrote:
> On Thu, Mar 03, 2016 at 11:52:02AM +0100, Michael Grzeschik wrote:
> > It is possible that da9052_ts_input_open is called and the touchscreen
> > is triggering continuous interrupts. In this case we will never leave
> > da9052_ts_input_open. The da9052_reg_update will never get the i2c bus
> > as the interrupt handler will continuously lock it.
> > 
> > This patch switch places of da9052_reg_update and the setting of
> > tsi->stopped. This way its ensured that da9052_ts_input_open will never
> > lockup on interrupt flood.
> 
> I understand what you are saying about updating register, however I do
> not understand why we would want to swap unmasking pendown event ans
> clearing the "stopped" flag.

The "stopped" flag has an locking purpose in the irq handler. My patch
ensures that the irq handler will not trigger any da9052_reg_update
before da9052_ts_input_open has finished.

On second thought, it would probably be enough to swap the call of
da9052_reg_update and da9052_enable_irq in da9052_ts_input_open.

This will have the same effect. I will send an corrected v2.

Thanks,
Michael

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