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

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Date:	Mon, 19 Aug 2013 19:12:38 +0200
From:	Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:	Zubair Lutfullah <zubair.lutfullah@...il.com>
Cc:	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

* 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
…
>+static irqreturn_t tiadc_irq(int irq, void *private)
>+{
…
>+		wake_up_interruptible(&adc_dev->wq_data_avail);
…
>+}
…
>+static irqreturn_t tiadc_trigger_h(int irq, void *p)
>+{
…
>+	schedule_work(&adc_dev->poll_work);
…
>+}
…
>+static void tiadc_adc_work(struct work_struct *work_s)
>+{
…
>+		wait_event_interruptible(adc_dev->wq_data_avail,
>+					(adc_dev->data_avail == 1));
…
>+}

This is not very nice. The problem is that you might sleep in a
workqueue and so the other jobs will wait until you are done. I'm think
it is better if you create your own worker here instead using the
system's.
I'm looking into DMA support for this so once your code is working it
should be possible to switch to DMA instead reading byte wise from the
fifo.
How did you test the whole thing? Do you have a test program which
selects a few sources and reads them in continuous mode?

Sebastian
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