Message-ID: <4CED0650.7030004@pengutronix.de>
Date: Wed, 24 Nov 2010 13:34:24 +0100
From: Marc Kleine-Budde <mkl@pengutronix.de>
Organization: Pengutronix
User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.1.15) Gecko/20101027 Thunderbird/3.0.10
MIME-Version: 1.0
To: Tomoya MORINAGA <tomoya-linux@dsn.okisemi.com>
CC: andrew.chih.howe.khor@intel.com, socketcan-core@lists.berlios.de,
        Samuel Ortiz <sameo@linux.intel.com>, margie.foster@intel.com,
        netdev@vger.kernel.org, Christian Pellegrin <chripell@fsfe.org>,
        linux-kernel@vger.kernel.org, yong.y.wang@intel.com,
        kok.howg.ewe@intel.com, joel.clark@intel.com,
        "David S. Miller" <davem@davemloft.net>,
        Wolfgang Grandegger <wg@grandegger.com>, qi.wang@intel.com
Subject: Re: [PATCH net-next-2.6 v3] can: Topcliff: PCH_CAN driver: Add Flow
 control,
References: <4CE2434B.5050701@dsn.okisemi.com>	<4CE27796.2000206@pengutronix.de>	<007401cb87b1$a773b3d0$66f8800a@maildom.okisemi.com>	<4CE64167.2030405@pengutronix.de> <003201cb8a02$f05b15e0$66f8800a@maildom.okisemi.com> <4CEA2986.4080607@pengutronix.de> <000b01cb8b6b$d7542a90$66f8800a@maildom.okisemi.com>
In-Reply-To: <000b01cb8b6b$d7542a90$66f8800a@maildom.okisemi.com>
Content-Type: multipart/signed; micalg=pgp-sha1;
 protocol="application/pgp-signature";
 boundary="------------enigD7C6F9C39BB5CE0F44C31FBA"
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 2726
Lines: 77

This is an OpenPGP/MIME signed message (RFC 2440 and 3156)
--------------enigD7C6F9C39BB5CE0F44C31FBA
Content-Type: text/plain; charset=ISO-8859-1
Content-Transfer-Encoding: quoted-printable

On 11/24/2010 01:09 AM, Tomoya MORINAGA wrote:
> On Monday, November 22, 2010 5:27 PM, Marc Kleine-Budde wrote:
>>>>>> Still we have the busy waiting in the TX path. Maybe you can move =
the
>>>>>> waiting before accessing the if[1] and remove the busy waiting her=
e.
>>>>> I can't understand your saying.
>>>>> For transmitting data, calling pch_can_rw_msg_obj is mandatory.
>>>> Yes, but the busy wait is not needed. It should be enough to do the
>>>> busy-waiting _before_ accessing the if[1].
>>>
>>> Do you mean we should create other pch_can_rw_msg_obj which doesn't h=
ave busy wait ?
>> ACK, and this non busy waiting is use in the TX path. But you add a bu=
sy
>> wait only function before accessing the if[1] in the TX path.
>=20
> The "busy waiting" of pch_can_rw_msg_obj is for next processing accesse=
s to Message object.
> If deleting this busy waiting, next processing can access to Message ob=
ject, regardless previous transfer doesn't
> complete yet.
> Thus, I think, the "busy waiting" is necessary.

Yes, it's necessary, but not where it is done currently.
Let me outline how I think the TX path should look like:

pch_xmit() {
	take_care_about_flow_control();
	prepare_can_frame_to_be_copied_to_tx_if();

	/* most likely we don't have to wait here */
	wait_until_tx_if_is_ready();

	copy_can_frame_to_tx_if();

	/* trigger tx in hardware */
	send_tx_if_but_dont_do_busywait();

	/* tx_if is busy now, but before we access it, we'll check tx_if is read=
y */
}

cheers, Marc

--=20
Pengutronix e.K.                  | Marc Kleine-Budde           |
Industrial Linux Solutions        | Phone: +49-231-2826-924     |
Vertretung West/Dortmund          | Fax:   +49-5121-206917-5555 |
Amtsgericht Hildesheim, HRA 2686  | http://www.pengutronix.de   |


--------------enigD7C6F9C39BB5CE0F44C31FBA
Content-Type: application/pgp-signature; name="signature.asc"
Content-Description: OpenPGP digital signature
Content-Disposition: attachment; filename="signature.asc"

-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1.4.10 (GNU/Linux)
Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org/

iEYEARECAAYFAkztBlQACgkQjTAFq1RaXHPr7ACeJkeg1kQ9oEK5RJh6XWb/xN0s
DykAnAlk9+t5/r5/GKblZq00KthubUtC
=M+Vn
-----END PGP SIGNATURE-----

--------------enigD7C6F9C39BB5CE0F44C31FBA--
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/