netdev - CAN-FD Transceiver Limitations

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Date:   Wed, 28 Jun 2017 17:14:42 -0500
From:   Franklin S Cooper Jr <fcooper@...com>
To:     <linux-can@...r.kernel.org>, <netdev@...r.kernel.org>,
        <wg@...ndegger.com>, <mkl@...gutronix.de>
Subject: CAN-FD Transceiver Limitations

Hi All,

The various CAN transceivers I've seen that support CAN-FD appear to be
fairly limited in terms of their supported max speed. I've seen some
transceivers that only support upto 2 Mbps while others support up to  5
Mbps. This is a problem when the SoC's CAN IP can support even higher
values than the transceiver.

Ideally I would think the MCAN driver should at the very least know what
the maximum speed supported by the transceiver it is connected to.
Therefore, either throwing an error if a request for a speed above the
transceiver capability or lower the requested speed to what ever the
transceiver is capability of doing.

In either case I do not know if it makes sense to add a DT property
within the MCAN driver or create another subnode that contains this
information. For example I see some ethernet drivers support
"fixed-link" subnode which is trying to solve a similar issue. Should I
go with that approach? If so would it make sense to reuse fixed-link
even though majority of its properties aren't applicable? Or should I
create something similar such as fixed-can-transceiver?