netdev - Re: [PATCH v2 2/4] can: fixed-transceiver: Add documentation for CAN fixed transceiver bindings

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Date:   Fri, 28 Jul 2017 10:41:40 +0200
From:   Oliver Hartkopp <socketcan@...tkopp.net>
To:     Franklin S Cooper Jr <fcooper@...com>,
        Andrew Lunn <andrew@...n.ch>, linux-kernel@...r.kernel.org,
        devicetree@...r.kernel.org, netdev@...r.kernel.org,
        linux-can@...r.kernel.org, wg@...ndegger.com, mkl@...gutronix.de,
        robh+dt@...nel.org, quentin.schulz@...e-electrons.com,
        sergei.shtylyov@...entembedded.com
Subject: Re: [PATCH v2 2/4] can: fixed-transceiver: Add documentation for CAN
 fixed transceiver bindings

On 07/28/2017 06:57 AM, Kurt Van Dijck wrote:

> So while _a_ transceiver may be spec'd to 1MBit during arbitration,
> CAN FD packets may IMHO exceed that speed during data phase.

When the bitrate is limited to 1Mbit/s you are ONLY allowed to use 
1Mbit/s in the data section too (either with CAN or CAN FD).

> That was the whole point of CAN FD: exceed the limits required for
> correct arbitration on transceiver & wire.

No. CAN FD is about a different frame format with up to 64 bytes AND the 
possibility to increase the bitrate in the data section of the frame.

> So I do not agree on the single bandwidth limitation.

The transceiver provides a single maximum bandwidth. It's an ISO Layer 1 
device.

> The word 'max-arbitration-bitrate' makes the difference very clear.

I think you are mixing up ISO layer 1 and ISO layer 2.

Regards,
Oliver