Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Date:   Sun, 16 Apr 2023 17:35:33 +0200
From:   Marc Kleine-Budde <mkl@pengutronix.de>
To:     Oliver Hartkopp <socketcan@hartkopp.net>
Cc:     Judith Mendez <jm@ti.com>,
        Chandrasekar Ramakrishnan <rcsekar@samsung.com>,
        Nishanth Menon <nm@ti.com>,
        Vignesh Raghavendra <vigneshr@ti.com>,
        Andrew Davis <afd@ti.com>,
        Wolfgang Grandegger <wg@grandegger.com>,
        Rob Herring <robh+dt@kernel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
        linux-can@vger.kernel.org, linux-kernel@vger.kernel.org,
        devicetree@vger.kernel.org, netdev@vger.kernel.org,
        Schuyler Patton <spatton@ti.com>
Subject: Re: [RFC PATCH 5/5] can: m_can: Add hrtimer to generate software
 interrupt
Message-ID: <20230416-failing-washbasin-e4fa5caea267-mkl@pengutronix.de>
References: <20230413223051.24455-1-jm@ti.com>
 <20230413223051.24455-6-jm@ti.com>
 <20230414-bounding-guidance-262dffacd05c-mkl@pengutronix.de>
 <4a6c66eb-2ccf-fc42-a6fc-9f411861fcef@hartkopp.net>
MIME-Version: 1.0
Content-Type: multipart/signed; micalg=pgp-sha512;
        protocol="application/pgp-signature"; boundary="howza2ulvftzwff5"
Content-Disposition: inline
In-Reply-To: <4a6c66eb-2ccf-fc42-a6fc-9f411861fcef@hartkopp.net>
Precedence: bulk


--howza2ulvftzwff5
Content-Type: text/plain; charset=utf-8
Content-Disposition: inline
Content-Transfer-Encoding: quoted-printable

On 16.04.2023 14:33:11, Oliver Hartkopp wrote:
>=20
>=20
> On 4/14/23 20:20, Marc Kleine-Budde wrote:
> > On 13.04.2023 17:30:51, Judith Mendez wrote:
> > > Add a hrtimer to MCAN struct. Each MCAN will have its own
> > > hrtimer instantiated if there is no hardware interrupt found.
> > >=20
> > > The hrtimer will generate a software interrupt every 1 ms. In
> >=20
> > Are you sure about the 1ms?

I had the 5ms that are actually used in the code in mind. But this is a
good calculation.

> The "shortest" 11 bit CAN ID CAN frame is a Classical CAN frame with DLC =
=3D 0
> and 1 Mbit/s (arbitration) bitrate. This should be 48 bits @1Mbit =3D> ~50
> usecs
>=20
> So it should be something about
>=20
>     50 usecs * (FIFO queue len - 2)

Where does the "2" come from?

> if there is some FIFO involved, right?

Yes, the mcan core has a FIFO. In the current driver the FIFO
configuration is done via device tree and fixed after that. And I don't
know the size of the available RAM in the mcan IP core on that TI SoC.

Marc

--=20
Pengutronix e.K.                 | Marc Kleine-Budde          |
Embedded Linux                   | https://www.pengutronix.de |
Vertretung N=C3=BCrnberg              | Phone: +49-5121-206917-129 |
Amtsgericht Hildesheim, HRA 2686 | Fax:   +49-5121-206917-9   |

--howza2ulvftzwff5
Content-Type: application/pgp-signature; name="signature.asc"

-----BEGIN PGP SIGNATURE-----

iQEzBAABCgAdFiEEDs2BvajyNKlf9TJQvlAcSiqKBOgFAmQ8FcAACgkQvlAcSiqK
BOiz7Qf9GVU38YyuModIpIhfmJ2wG+iWBhXzfO/pbD4ifYxknz+DcL1zgpTBGCrX
wWjHojZuQQPU9AE9UT7vjKfQOcJs90kMFOmI87bEHQLUl8fO40PekZradALAVEII
GEIFnU8ArKzXjaaUJxCmahRP/7cHPjctxRdn10RWkeFW5lITOiiO3rwOrLVogeVe
9KX17fQQ2GbRiIT2e6GNWjngkAgsWo77hqtrSdJr8wvJQZ82Xkct9BCr14dJeoz1
bgMiqIiELi+8hG0Sx2G+hdY+/30pXllBV4LFYluPY4JUjS9GeEWC6r7wGF0HqGe9
FW2ZiemY+PGYXCB67pbf+f8SPAiQvg==
=QN1Y
-----END PGP SIGNATURE-----

--howza2ulvftzwff5--