linux-kernel - Re: [PATCH] platform/x86: thinkpad

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Message-Id: <c05afb18-bca5-4500-877d-d44ef3abc310@app.fastmail.com>
Date:   Wed, 13 Sep 2023 12:41:42 -0400
From:   "Mark Pearson" <mpearson-lenovo@...ebb.ca>
To:     "Hans de Goede" <hdegoede@...hat.com>,
        "Fernando Eckhardt Valle" <fevalle@....br>,
        "Henrique de Moraes Holschuh" <hmh@....eng.br>,
        "markgross@...nel.org" <markgross@...nel.org>,
        ibm-acpi-devel@...ts.sourceforge.net,
        "platform-driver-x86@...r.kernel.org" 
        <platform-driver-x86@...r.kernel.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] platform/x86: thinkpad_acpi: sysfs interface to auxmac

On Wed, Sep 13, 2023, at 11:58 AM, Hans de Goede wrote:
> Hi Fernando,
>
> On 9/6/23 21:52, Fernando Eckhardt Valle wrote:
>> Newer Thinkpads have a feature called Mac Address Passthrough.
>> This patch provides a sysfs interface that userspace can use
>> to get this auxiliary mac address.
>> 
>> Signed-off-by: Fernando Eckhardt Valle <fevalle@....br>
>
> Thank you for your patch. 
>
> At a minimum for this patch to be accepted you will need
> to document the new sysfs interface in:
>
> Documentation/admin-guide/laptops/thinkpad-acpi.rst
>
> But I wonder if we should export this information to
> userspace in this way ?
>
> The reason why I'm wondering is because mac-address passthrough
> in case of using e.g. Lenovo Thunderbolt docks is already
> supported by the kernel by code for this in drivers/net/usb/r8152.c :
>
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/net/usb/r8152.c#n1613
>
> So I'm wondering if we really need this, is there a planned
> userspace API consumer of the new sysfs interface ?
>
> Or is this only intended as a way for a user to query this, iow
> is this purely intended for informational purposes ?
>
Hi Hans,

We've previously had strong pushback from the maintainers in the net tree that the MAC passthru should not be done there and should be done in user-space. I'd have to dig up the threads, but there was a preference for it to not be done in the kernel (and some frustrations at having vendor specific changes in the net driver).

We've also seen various timing issues (some related to ME FW doing it's thing) that makes it tricky to handle in the kernel - with added delays being needed leading to patches that can't be accepted.

This approach is one of the steps towards fixing this. Fernando did discuss and review this with me beforehand (apologies - I meant to add a note saying I'd been involved). If you think there is a better approach please let us know, but we figured as this is a Lenovo specific thing it made sense to have it here in thinkpad_acpi.

There will be a consumer (I think it's a script and udev rule) to update the MAC if a passthru-MAC address is provided via the BIOS. This will be open-source, but we haven't really figured out how to release it yet.

Fernando - please correct anything I've gotten wrong!

Mark