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From: Oliver Hartkopp <socketcan-fJ+pQTUTwRTk1uMJSBkQmQ@public.gmane.org>
To: Wolfgang Grandegger <wg-5Yr1BZd7O62+XT7JhA+gdA@public.gmane.org>
Cc: andrew.chih.howe.khor-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org,
	socketcan-core-0fE9KPoRgkgATYTw5x5z8w@public.gmane.org,
	qi.wang-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org,
	netdev-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
	gregkh-l3A5Bk7waGM@public.gmane.org,
	yong.y.wang-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org,
	Masayuki Ohtake
	<masa-korg-ECg8zkTtlr0C6LszWs/t0g@public.gmane.org>,
	Marc Kleine-Budde <mkl-bIcnvbaLZ9MEGnE8C9+IrQ@public.gmane.org>,
	Morinaga <morinaga526-ECg8zkTtlr0C6LszWs/t0g@public.gmane.org>,
	meego-dev-WXzIur8shnEAvxtiuMwx3w@public.gmane.org,
	arjan-VuQAYsv1563Yd54FQh9/CA@public.gmane.org
Subject: Re: [MeeGo-Dev][PATCH] Topcliff: Update PCH_CAN driver to 2.6.35
Date: Wed, 15 Sep 2010 11:42:48 +0200	[thread overview]
Message-ID: <4C909518.5010309@hartkopp.net> (raw)
In-Reply-To: <4C9078D3.50300-5Yr1BZd7O62+XT7JhA+gdA@public.gmane.org>

On 15.09.2010 09:42, Wolfgang Grandegger wrote:
> On 09/14/2010 02:46 AM, Masayuki Ohtake wrote:
>> Hi Marc,
>>
>>>>> - implement NAPI
>>>> Since Topcliff CAN HW register has only single rx buffer,
>>>> I think NAPI is unnecessary.
>>
>>> Doesn't matter. Please try to implement it.
>>
>> Our CAN driver must pull received data from CAN-HW rx buffer as fast as it can
>> so that the received data is not over-written by next received data.
>> In case of implemented with NAPI,
>> since NAPI has time-lagging after receiving first packet,
>> probability of over-written(discarded) buffer is to be high.
>> Thus, for our CAN HW, we should NOT implement with NAPI but normal "netif_rx".
> 
> True, if you just use one RX-Object. But it just helps a little bit and
> it would be much better to use the buffering on RX messages in the CAN
> controller hardware, either by using more than one RX object, or
> combining RX objects to a FIFO, or whatever your CAN controller supports.

Good point!

As long as the order of the received CAN frames is not shuffled (-> plain FIFO
behaviour) using more than one RX buffer is a good idea.

Just a remark:

During the IDF the informations about the Topcliff Controller Hub have been
reworked, so that some of the documentation became available for the public:

http://edc.intel.com/Platforms/Atom-E6xx/#hardware

Especially the Datasheet for the Platform Controller Hub EG20T can be found:

http://download.intel.com/embedded/chipsets/datasheet/324211.pdf

In chapter 13 there are some details about the CAN controller.

Regards,
Oliver

  parent reply	other threads:[~2010-09-15  9:42 UTC|newest]

Thread overview: 40+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2010-08-11  0:25 [MeeGo-Dev][PATCH] Topcliff: Update PCH_CAN driver to 2.6.35 Masayuki Ohtak
     [not found] ` <4C61EDE5.4030505-ECg8zkTtlr0C6LszWs/t0g@public.gmane.org>
2010-08-11 10:37   ` Daniel Baluta
2010-08-12  1:42     ` Wang, Qi
2010-08-12  2:04       ` Greg KH
2010-08-12  2:13         ` Wang, Qi
     [not found]         ` <20100812020414.GD14121-l3A5Bk7waGM@public.gmane.org>
2010-08-12  6:25           ` Oliver Hartkopp
2010-08-12  6:29             ` Wang, Qi
2010-08-12  2:39       ` Masayuki Ohtake
     [not found]       ` <D5AB6E638E5A3E4B8F4406B113A5A19A28EA26EB-QQHDSDV1ERZpB2pF5aRoyrfspsVTdybXVpNB7YpNyf8@public.gmane.org>
2010-08-12  5:17         ` Daniel Baluta
2010-08-12  9:03         ` Wolfgang Grandegger
2010-08-13  0:23           ` Wang, Qi
     [not found]             ` <D5AB6E638E5A3E4B8F4406B113A5A19A28EA2AB1-QQHDSDV1ERZpB2pF5aRoyrfspsVTdybXVpNB7YpNyf8@public.gmane.org>
2010-08-13  6:11               ` Daniel Baluta
2010-08-13 10:58               ` Wolfgang Grandegger
2010-08-20  6:01                 ` Masayuki Ohtake
     [not found]                   ` <000f01cb402d$34b675b0$66f8800a-a06+6cuVnkTSQfdrb5gaxUEOCMrvLtNR@public.gmane.org>
2010-08-20  7:59                     ` Wolfgang Grandegger
2010-08-20  8:37                       ` Masayuki Ohtake
2010-08-11 12:31   ` Wolfgang Grandegger
     [not found]     ` <D5AB6E638E5A3E4B8F4406B113A5A19A28EA26CC@shsmsx501.ccr.corp.intel.com>
     [not found]       ` <4C63B6C9.5050804@grandegger.com>
     [not found]         ` <D5AB6E638E5A3E4B8F4406B113A5A19A28EA29DF@shsmsx501.ccr.corp.intel.com>
2010-09-01  7:45           ` Masayuki Ohtake
2010-09-01 17:04             ` out-of-order tx objects - was " Oliver Hartkopp
2010-09-01 17:04               ` Oliver Hartkopp
2010-09-01 18:51             ` Wolfgang Grandegger
2010-09-01 18:51               ` Wolfgang Grandegger
2010-09-02  3:19               ` Masayuki Ohtake
2010-09-02  3:19                 ` Masayuki Ohtake
2010-09-02  6:32                 ` Wolfgang Grandegger
2010-09-02  6:32                   ` Wolfgang Grandegger
2010-08-11 13:04   ` Marc Kleine-Budde
2010-09-13 12:07     ` Masayuki Ohtake
     [not found]       ` <005f01cb533e$5c21d530$66f8800a-a06+6cuVnkTSQfdrb5gaxUEOCMrvLtNR@public.gmane.org>
2010-09-13 12:29         ` Marc Kleine-Budde
2010-09-14  0:46           ` Masayuki Ohtake
2010-09-14  7:08             ` Marc Kleine-Budde
     [not found]             ` <003a01cb53a6$4ca724d0$66f8800a-a06+6cuVnkTSQfdrb5gaxUEOCMrvLtNR@public.gmane.org>
2010-09-15  7:42               ` Wolfgang Grandegger
     [not found]                 ` <4C9078D3.50300-5Yr1BZd7O62+XT7JhA+gdA@public.gmane.org>
2010-09-15  9:42                   ` Oliver Hartkopp [this message]
2010-09-15 10:55                     ` Wolfgang Grandegger
2010-09-15 12:04                       ` Marc Kleine-Budde
2010-09-15 12:11                         ` Wolfgang Grandegger
2010-09-13 15:22         ` Greg KH
2010-09-14  8:48           ` Masayuki Ohtake
     [not found]             ` <00ca01cb53e9$a50c1930$66f8800a-a06+6cuVnkTSQfdrb5gaxUEOCMrvLtNR@public.gmane.org>
2010-09-14 13:10               ` Greg KH
2010-09-15  1:21                 ` Masayuki Ohtake

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