linux-kernel - Re: [PATCH 0/8] greybus: support point-to-point topology

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Message-Id: <DG0C329Q24U8.2959NJ9J9KXV4@silabs.com>
Date: Wed, 28 Jan 2026 10:39:38 -0500
From: Damien Riégel <damien.riegel@...abs.com>
To: "Greg Kroah-Hartman" <gregkh@...uxfoundation.org>,
        Damien Riégel <damien.riegel@...abs.com>
Cc: <greybus-dev@...ts.linaro.org>, <linux-kernel@...r.kernel.org>,
        "Johan
 Hovold" <johan@...nel.org>, "Alex Elder" <elder@...nel.org>,
        <linux-devel@...abs.com>
Subject: Re: [PATCH 0/8] greybus: support point-to-point topology

On Wed Jan 28, 2026 at 1:04 AM EST, Greg Kroah-Hartman wrote:
> On Tue, Jan 27, 2026 at 03:23:44PM -0500, Damien Riégel wrote:
>> On Fri Jan 16, 2026 at 10:09 AM EST, Greg Kroah-Hartman wrote:
>> [...]
>>
>> >>
>> >> The SVC doesn' really serve a purpose here, as there is no bus to
>> >> manage, and adding its support only increase the complexity and the code
>> >> size needed on memory-constrained devices.
>> >
>> > Exactly how much memory does a "single point" SVC driver take, vs.
>> > adding new P2P functionality everywhere in the code like you just did?
>> > Finding that out would be good first before worrying about adding
>> > another type of "bus" here please.
>>
>> Sorry for not giving numbers in the cover letter. We measured 10kB of
>> code size difference (which may be on the higher end of the spectrum)
>> and in Zephyr [1] they measured a 2kB difference (which is probably on
>> the lower end considering the implementation is pretty barebone).
>
> Please submit your "empty" SVC driver, 10kb seems too big to me, I think
> we can slim it down, or at the very least, see what is making it "large"
> and potentially work to reduce that.

The comparison I did originally was pretty naive. When I tested without
the SVC, the C files were not even compiled. What I didn't account for
is that our SVC currently logs pretty extensively, and guess where these
log strings are stored...

After removing the logs, I could compare apples to apples:
 - with SVC: 59,272 B
 - without SVC: 57,556 B

So not even 2kB difference.

> For Zephyr, I thought it was 1kb in the github comments, but still 2kb
> seems reasonable :)

The last comment in the thread says 2kB, but it's in the same ballpark.

So I think we have our number, an empty SVC would be in the 1kB to 2kB
range.