Re: [PATCH 15/17] media: st_rc: Don't stay on an IRQ handler forever

[Mauro Carvalho Chehab <mchehab@s-opensource.com>]

Em Fri, 13 Apr 2018 11:15:16 +0200
Mason <slash.tmp@free.fr> escreveu:

> On 12/04/2018 17:24, Mauro Carvalho Chehab wrote:
> 
> > As warned by smatch:
> > 	drivers/media/rc/st_rc.c:110 st_rc_rx_interrupt() warn: this loop depends on readl() succeeding
> > 
> > If something goes wrong at readl(), the logic will stay there
> > inside an IRQ code forever. This is not the nicest thing to
> > do :-)
> > 
> > So, add a timeout there, preventing staying inside the IRQ
> > for more than 10ms.
> > 
> > Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
> > ---
> >  drivers/media/rc/st_rc.c | 16 ++++++++++------
> >  1 file changed, 10 insertions(+), 6 deletions(-)
> > 
> > diff --git a/drivers/media/rc/st_rc.c b/drivers/media/rc/st_rc.c
> > index d2efd7b2c3bc..c855b177103c 100644
> > --- a/drivers/media/rc/st_rc.c
> > +++ b/drivers/media/rc/st_rc.c
> > @@ -96,19 +96,24 @@ static void st_rc_send_lirc_timeout(struct rc_dev *rdev)
> >  
> >  static irqreturn_t st_rc_rx_interrupt(int irq, void *data)
> >  {
> > +	unsigned long timeout;
> >  	unsigned int symbol, mark = 0;
> >  	struct st_rc_device *dev = data;
> >  	int last_symbol = 0;
> > -	u32 status;
> > +	u32 status, int_status;
> >  	DEFINE_IR_RAW_EVENT(ev);
> >  
> >  	if (dev->irq_wake)
> >  		pm_wakeup_event(dev->dev, 0);
> >  
> > -	status  = readl(dev->rx_base + IRB_RX_STATUS);
> > +	/* FIXME: is 10ms good enough ? */
> > +	timeout = jiffies +  msecs_to_jiffies(10);
> > +	do {
> > +		status  = readl(dev->rx_base + IRB_RX_STATUS);
> > +		if (!(status & (IRB_FIFO_NOT_EMPTY | IRB_OVERFLOW)))
> > +			break;
> >  
> > -	while (status & (IRB_FIFO_NOT_EMPTY | IRB_OVERFLOW)) {
> > -		u32 int_status = readl(dev->rx_base + IRB_RX_INT_STATUS);
> > +		int_status = readl(dev->rx_base + IRB_RX_INT_STATUS);
> >  		if (unlikely(int_status & IRB_RX_OVERRUN_INT)) {
> >  			/* discard the entire collection in case of errors!  */
> >  			ir_raw_event_reset(dev->rdev);
> > @@ -148,8 +153,7 @@ static irqreturn_t st_rc_rx_interrupt(int irq, void *data)
> >  
> >  		}
> >  		last_symbol = 0;
> > -		status  = readl(dev->rx_base + IRB_RX_STATUS);
> > -	}
> > +	} while (time_is_after_jiffies(timeout));
> >  
> >  	writel(IRB_RX_INTS, dev->rx_base + IRB_RX_INT_CLEAR);
> >    
> 
> Isn't this a place where the iopoll.h helpers might be useful?
> 
> e.g. readl_poll_timeout()
> 
> https://elixir.bootlin.com/linux/latest/source/include/linux/iopoll.h#L114

That won't work. Internally[1], readx_poll_timeout() calls
usleep_range().

[1] https://elixir.bootlin.com/linux/latest/source/include/linux/iopoll.h#L43

It can't be called here, as this loop happens at the irq
handler.

Thanks,
Mauro