netdev - Re: CAN-FD Transceiver Limitations

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Message-ID: <d5c2e2f2-8b74-58e1-0cc8-727ba39bd14c@ti.com>
Date:   Thu, 29 Jun 2017 18:14:46 -0500
From:   Franklin S Cooper Jr <fcooper@...com>
To:     Andrew Lunn <andrew@...n.ch>, <linux-can@...r.kernel.org>,
        <netdev@...r.kernel.org>, <wg@...ndegger.com>,
        <mkl@...gutronix.de>, <devicetree@...r.kernel.org>
Subject: Re: CAN-FD Transceiver Limitations



On 06/29/2017 05:36 PM, Kurt Van Dijck wrote:
>>>>
>>>> mcan@0 {
>>>> 	...
>>>> 	fixed-transceiver {
>>>> 	      max-canfd-speed = <2000>
>>>> 	};
>>>> 	...
>>>> };
> 
> Since when would a transceiver support different speeds for CAN & CANFD?

When I say CAN I'm referring to CAN 2.0 specification which mentioned
speeds upto 1 Mbit/s. While CAN FD supports higher bitrates.

> No transceivers were available, but they are now.
> I see no datalink problem applying 2MBit for regular CAN with apropriate
> physical layer, and CAN does not predefine the physical layer
> (advise != define).
> 
> IMHO,
> 	fixed-transceiver {
> 		max-arbitration-speed = <2000000>
> 		max-data-speed = <4000000>
> 	};
> is way better to describe the hardware.
> Regular CAN chips would not consider max-data-speed...

What is arbitration speed?

Also if I understand you correctly then I agree drivers for traditional
CAN wouldn't care about this subnode. Although it may be helpful for
max-data-speed to become max-canfd-speed or something along those lines.
Just so the property's purpose is clear.
> 
> Kind regards,
> Kurt
>