netdev - Re: [PATCH v2 0/6] can: slcan: extend supported features (step 2)

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Date:   Mon, 25 Jul 2022 15:25:14 +0200
From:   Marc Kleine-Budde <mkl@...gutronix.de>
To:     Dario Binacchi <dario.binacchi@...rulasolutions.com>
Cc:     linux-kernel@...r.kernel.org, michael@...rulasolutions.com,
        Amarula patchwork <linux-amarula@...rulasolutions.com>,
        Jeroen Hofstee <jhofstee@...tronenergy.com>,
        Oliver Hartkopp <socketcan@...tkopp.net>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Wolfgang Grandegger <wg@...ndegger.com>,
        linux-can@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [PATCH v2 0/6] can: slcan: extend supported features (step 2)

On 25.07.2022 08:54:13, Dario Binacchi wrote:
> With this series I try to finish the task, started with the series [1],
> of completely removing the dependency of the slcan driver from the
> userspace slcand/slcan_attach applications.
> 
> The series, however, still lacks a patch for sending the bitrate setting
> command to the adapter:
> 
> slcan_attach -b <btr> <dev>
> 
> Without at least this patch the task cannot be considered truly completed.
> 
> The idea I got is that this can only happen through the ethtool API.
> Among the various operations made available by this interface I would
> have used the set_regs (but only the get_regs has been developed), or,
> the set_eeprom, even if the setting would not be stored in an eeprom.
> IMHO it would take a set_regs operation with a `struct ethtool_wregs'
> parameter similar to `struct ethtool_eeprom' without the magic field:

This doesn't feel right.

> struct ethtool_wregs {
> 	__u32	cmd;
> 	__u32	offset;
> 	__u32	len;
> 	__u8	data[0];
> };
> 
> But I am not the expert and if there was an alternative solution already
> usable, it would be welcome.

Have a look at the get/set_tunable() callback:

| https://elixir.bootlin.com/linux/latest/source/include/linux/ethtool.h#L575

You probably have to add a new tunable. Here you'll find the people and
commits that changed the tunable:

| https://github.com/torvalds/linux/blame/master/include/uapi/linux/ethtool.h#L229

It's usually worth including them in an RFC patch series where you add a
new tunable and make use of it in the slcan driver.

regards,
Marc

-- 
Pengutronix e.K.                 | Marc Kleine-Budde           |
Embedded Linux                   | https://www.pengutronix.de  |
Vertretung West/Dortmund         | Phone: +49-231-2826-924     |
Amtsgericht Hildesheim, HRA 2686 | Fax:   +49-5121-206917-5555 |

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