Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Date:   Tue, 13 Oct 2020 14:58:51 -0400
From:   William Breathitt Gray <vilhelm.gray@gmail.com>
To:     David Lechner <david@lechnology.com>
Cc:     Pavel Machek <pavel@ucw.cz>, jic23@kernel.org,
        kamel.bouhara@bootlin.com, gwendal@chromium.org,
        alexandre.belloni@bootlin.com, linux-iio@vger.kernel.org,
        linux-kernel@vger.kernel.org,
        linux-stm32@st-md-mailman.stormreply.com,
        linux-arm-kernel@lists.infradead.org, syednwaris@gmail.com,
        patrick.havelange@essensium.com, fabrice.gasnier@st.com,
        mcoquelin.stm32@gmail.com, alexandre.torgue@st.com
Subject: Re: [PATCH v5 4/5] docs: counter: Document character device interface
Message-ID: <20201013185851.GB32722@shinobu>
References: <cover.1601170670.git.vilhelm.gray@gmail.com>
 <54190f9875b81b6aa5483a7710b084053a44abb8.1601170670.git.vilhelm.gray@gmail.com>
 <20201008080909.GA31561@amd>
 <20201008122845.GA3314@shinobu>
 <d06d5e47-5776-85ee-0dc5-8b624e36d83d@lechnology.com>
MIME-Version: 1.0
Content-Type: multipart/signed; micalg=pgp-sha512;
        protocol="application/pgp-signature"; boundary="5/uDoXvLw7AC5HRs"
Content-Disposition: inline
In-Reply-To: <d06d5e47-5776-85ee-0dc5-8b624e36d83d@lechnology.com>
Precedence: bulk


--5/uDoXvLw7AC5HRs
Content-Type: text/plain; charset=utf-8
Content-Disposition: inline
Content-Transfer-Encoding: quoted-printable

On Mon, Oct 12, 2020 at 12:04:10PM -0500, David Lechner wrote:
> On 10/8/20 7:28 AM, William Breathitt Gray wrote:
> > On Thu, Oct 08, 2020 at 10:09:09AM +0200, Pavel Machek wrote:
> >> Hi!
> >>
> >>> +        int main(void)
> >>> +        {
> >>> +                struct pollfd pfd =3D { .events =3D POLLIN };
> >>> +                struct counter_event event_data[2];
> >>> +
> >>> +                pfd.fd =3D open("/dev/counter0", O_RDWR);
> >>> +
> >>> +                ioctl(pfd.fd, COUNTER_SET_WATCH_IOCTL, watches);
> >>> +                ioctl(pfd.fd, COUNTER_SET_WATCH_IOCTL, watches + 1);
> >>> +                ioctl(pfd.fd, COUNTER_LOAD_WATCHES_IOCTL);
> >>> +
> >>> +                for (;;) {
> >>> +                        poll(&pfd, 1, -1);
> >>
> >> Why do poll, when you are doing blocking read?
> >>
> >>> +                        read(pfd.fd, event_data,  sizeof(event_data)=
);
> >>
> >> Does your new chrdev always guarantee returning complete buffer?
> >>
> >> If so, should it behave like that?
> >>
> >> Best regards,
> >> 									Pavel
> >> --=20
> >> (english) http://www.livejournal.com/~pavelmachek
> >> (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horse=
s/blog.html
> >=20
> > I suppose you're right: a poll() should be redundant now with this
> > version of the character device implementation because buffers will
> > always return complete; so a blocking read() should achieve the same
> > behavior that a poll() with read() would.
> >=20
> > I'll give some more time for additional feedback to come in for this
> > version of the patchset, and then likely remove support for poll() in
> > the v6 submission.
> >=20
> > William Breathitt Gray
> >=20
>=20
> I hope that you mean that you will just remove it from the example
> and not from the chardev. Otherwise it won't be possible to
> integrate this with an event loop.

Would you elaborate a bit further on this? My thought process is that
because users must set the Counter Events they want to watch, and only
those Counter Events show up in the character device node, a blocking
read() would effectively behave the same as poll() with read(); if none
of the Counter Events occur, the read() just blocks until one does, thus
making the use of a poll() call redundant.

William Breathitt Gray

--5/uDoXvLw7AC5HRs
Content-Type: application/pgp-signature; name="signature.asc"

-----BEGIN PGP SIGNATURE-----
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=bg3S
-----END PGP SIGNATURE-----

--5/uDoXvLw7AC5HRs--