From: Marc Kleine-Budde <mkl@pengutronix.de>
To: David Jander <david@protonic.nl>
Cc: wg@grandegger.com, linux-can@vger.kernel.org
Subject: Re: [PATCH 2/3] can: flexcan.c: Re-write receive path to use MB queue instead of FIFO
Date: Tue, 02 Sep 2014 16:53:46 +0200 [thread overview]
Message-ID: <5405D9FA.6050207@pengutronix.de> (raw)
In-Reply-To: <20140902140407.1ee9db68@archvile>
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On 09/02/2014 02:04 PM, David Jander wrote:
> On Tue, 02 Sep 2014 13:30:24 +0200
> Marc Kleine-Budde <mkl@pengutronix.de> wrote:
>
>> On 08/27/2014 11:58 AM, David Jander wrote:
>>> The FlexCAN controller has a RX FIFO that is only 6 messages deep, and a
>>> mailbox space capable of holding up to 63 messages.
>>> This space was largely unused, limiting the permissible latency from
>>> interrupt to NAPI to only 6 messages. This patch uses all available MBs
>>> for message reception and frees the MBs in the IRQ handler to greatly
>>> decrease the likelihood of receive overruns.
>>
>> What about the order of the incoming CAN frames? Is it still preserved?
>
> Yes, it is preserved as long as latency doesn't exceed 30 frames, which is
> way more than the original driver could take. The algorithm is not trivial,
> therefor I included an explanatory comment to flexcan_copy_rxmbs().
To be honest, I haven't looked at the algorithm in detail. I think we
first have to fix both bugs (the errata and the mailbox initialization
issue).
>> You make use of the CTRL2 register, which is not present on some older
>> (but supported) flexcan IP cores. You increase FLEXCAN_MCR_MAXMB to
>> 0x40, which is not supported on older IPs. The register rximr, is also
>> not present on older cores. Don't break support for the older CAN cores.
>
> Oops. Thanks for pointing that out. I will check the reference manual of the
> i.MX53 (which should have be the oldest supported version of this IP core,
> right?). Of course I do not want to break older CAN cores.
> I will check correctness testing the code on an i.MX28 board which I have.
Regarding the versions of the IP cores, we should not trust them, as
they are not public available..
Marc
--
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 |
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next prev parent reply other threads:[~2014-09-02 14:53 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-08-27 9:58 [PATCH 0/3] Decrease likelyhood of RX overruns David Jander
2014-08-27 9:58 ` [PATCH 1/3] can: flexcan.c: Correctly initialize mailboxes David Jander
2014-09-02 10:24 ` Marc Kleine-Budde
2014-09-02 10:37 ` David Jander
2014-09-02 10:59 ` Marc Kleine-Budde
2014-09-02 11:15 ` David Jander
2014-09-02 13:54 ` Marc Kleine-Budde
2014-09-02 14:27 ` David Jander
2014-09-02 11:32 ` David Jander
2014-09-02 11:38 ` Marc Kleine-Budde
2014-09-02 14:53 ` Marc Kleine-Budde
2014-08-27 9:58 ` [PATCH 2/3] can: flexcan.c: Re-write receive path to use MB queue instead of FIFO David Jander
2014-09-02 11:30 ` Marc Kleine-Budde
2014-09-02 12:04 ` David Jander
2014-09-02 14:53 ` Marc Kleine-Budde [this message]
2014-09-03 7:19 ` David Jander
2014-09-03 9:12 ` Marc Kleine-Budde
2014-09-03 15:42 ` David Jander
2014-08-27 9:58 ` [PATCH 3/3] can: flexcan.c: Implement last step of workaround for errata ERR005829 David Jander
2014-09-02 11:28 ` Marc Kleine-Budde
2014-09-02 11:36 ` David Jander
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