From: Sven Van Asbroeck <thesven73@gmail.com>
To: Jonathan Cameron <jic23@kernel.org>
Cc: Robert Eshleman <bobbyeshleman@gmail.com>,
Hartmut Knaack <knaack.h@gmx.de>,
Lars-Peter Clausen <lars@metafoo.de>,
Peter Meerwald-Stadler <pmeerw@pmeerw.net>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
linux-iio@vger.kernel.org
Subject: Re: [PATCH 1/3] iio: light: Add driver for ap3216c
Date: Mon, 11 Feb 2019 17:30:18 -0500 [thread overview]
Message-ID: <CAGngYiV_6MzKOSomAWs1znp8ThPRAL-e2CVZfn+ZHZOq8DiD0A@mail.gmail.com> (raw)
In-Reply-To: <20190211212734.01909e62@archlinux>
On Mon, Feb 11, 2019 at 4:27 PM Jonathan Cameron <jic23@kernel.org> wrote:
>
> Agreed. Or potentially just use regmap_bulk_read and rely on
> the regmap internal locking to do it for you.
Neat solution. But it may only work correctly iff regmap_bulk_read()
reads the low
address first. I'm not sure if this function has that guarantee. If
somebody changes
the read order, the driver will break. But I think I'm being overly
paranoid here :)
> So yes, it's more than possible that userspace won't get the same number
> of events as samples taken over the limit, but I don't know why we care.
> We can about missing a threshold being passed entirely, not about knowing
> how many samples we were above it for.
I suspect that we run a small risk of losing an event, like so:
PS (12.5 ms)
--> interrupt -> iio event
ALS (100 ms)
--> interrupt -> iio event
PS (12.5 ms)
--> interrupt ========= no iio event generated
ALS (100 ms)
--> interrupt -> iio event
To see why, imagine that the scheduler decides to move away from the
threaded interrupt
handler right before ap3216c_clear_int(). Say 20ms, which I know is a
loooong time,
but bear with me, the point is that it _could_ happen as we're not a RTOS.
static irqreturn_t ap3216c_event_handler(int irq, void *p)
{
/* imagine ALS interrupt came in, INT_STATUS is 0b01 */
regmap_read(data->regmap, AP3216C_INT_STATUS, &status);
if (status & mask1) iio_push_event(PROX);
if (status & mask2) iio_push_event(LIGHT);
/* imagine schedule happens here */
msleep(20);
/* while we were not running, PS interrupt came in
INT_STATUS is now 0b11
yet no new interrupt is generated, as we are ONESHOT
*/
ap3216c_clear_int(data);
/* clears both bits, interrupt line goes low.
knowledge that the PS interrupt came in is now lost */
}
Not sure if that's acceptable driver behaviour. In real life it
probably wouldn't matter much,
except for occasional added latency maybe ?
next prev parent reply other threads:[~2019-02-11 22:30 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-02-10 20:36 [PATCH 1/3] iio: light: Add driver for ap3216c Robert Eshleman
2019-02-10 20:39 ` [PATCH 3/3] dt-bindings: iio: light: Add ap3216c Robert Eshleman
2019-02-11 14:58 ` [PATCH 1/3] iio: light: Add driver for ap3216c Peter Meerwald-Stadler
2019-02-13 16:33 ` Robert Eshleman
2019-02-11 19:09 ` Sven Van Asbroeck
2019-02-11 21:27 ` Jonathan Cameron
2019-02-11 22:30 ` Sven Van Asbroeck [this message]
2019-02-12 20:47 ` Jonathan Cameron
2019-02-13 4:40 ` Sven Van Asbroeck
2019-02-13 4:56 ` Sven Van Asbroeck
2019-02-18 15:16 ` Jonathan Cameron
2019-02-18 19:35 ` Sven Van Asbroeck
2019-02-20 12:32 ` Jonathan Cameron
2019-02-20 15:09 ` Sven Van Asbroeck
2019-02-13 16:18 ` Robert Eshleman
2019-02-11 19:29 ` Sven Van Asbroeck
2019-02-13 2:17 ` Robert Eshleman
2019-02-13 3:25 ` Sven Van Asbroeck
2019-02-18 15:22 ` Jonathan Cameron
2019-02-18 17:13 ` Sven Van Asbroeck
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