linux-kernel - Re: [PATCH 4/4] iio: ti_am335x_adc: Add continuous sampling and trigger support

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Date:	Fri, 16 Aug 2013 22:13:29 +0100
From:	"Zubair Lutfullah :" <zubair.lutfullah@...il.com>
To:	Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc:	Zubair Lutfullah <zubair.lutfullah@...il.com>, jic23@....ac.uk,
	dmitry.torokhov@...il.com, linux-iio@...r.kernel.org,
	linux-input@...r.kernel.org, linux-kernel@...r.kernel.org,
	gregkh@...uxfoundation.org, Russ.Dill@...com
Subject: Re: [PATCH 4/4] iio: ti_am335x_adc: Add continuous sampling and
 trigger support

On Fri, Aug 16, 2013 at 03:25:49PM +0200, Sebastian Andrzej Siewior wrote:
> * Zubair Lutfullah | 2013-08-13 21:05:03 [+0100]:
> 
> >diff --git a/drivers/iio/adc/ti_am335x_adc.c b/drivers/iio/adc/ti_am335x_adc.c
> >index 3ceac3e..0d7e313 100644
> >--- a/drivers/iio/adc/ti_am335x_adc.c
> >+++ b/drivers/iio/adc/ti_am335x_adc.c
> >@@ -141,58 +350,51 @@ static int tiadc_read_raw(struct iio_dev *indio_dev,
> > {
> …
> >+	if (iio_buffer_enabled(indio_dev))
> >+		return -EBUSY;
> >+	else {
> 
> You can drop else so you lose one ident level.
> 
Noted.

> >+		unsigned long timeout = jiffies + usecs_to_jiffies
> >+					(IDLE_TIMEOUT * adc_dev->channels);
> 
> What computing this once? ->channels is assigned at probe time.
> 
The timeout depends on number of SW enabled channels.
Hence the calculation. In this read_raw, one channel is to be
read. 
However, all channels are sampled. And the one that the 
userspace requires is pushed to user.

> >+		/* Wait for ADC sequencer to complete sampling */
> >+		while (tiadc_readl(adc_dev, REG_ADCFSM) & SEQ_STATUS) {
> >+			if (time_after(jiffies, timeout))
> >+				return -EAGAIN;
> 
> You should check the condition after the timeout occured once again. It
> is possible that the task performing the read has been pushed away by a
> higher prio task (or preempted incase this sounds like a bully) and
> after it got back on the cpu the timeout occured but the condition is
> valid and no reason for -EAGAIN.
> 
> Sebastian

Interesting catch. I'll look into it.

Thanks for pointing it out.

Zubair
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