linux-kernel - Re: [PATCH] arm64: defconfig: Build STMMAC Ethernet driver into the kernel for NFS boot

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Message-ID: <kjotbgwqlvl4uv4bcynqsiynf4dsoplw3szaqlcfd7rm7k633p@64c552v3llz2>
Date: Thu, 12 Jun 2025 16:30:32 +0200
From: Thierry Reding <thierry.reding@...il.com>
To: Geert Uytterhoeven <geert@...ux-m68k.org>
Cc: Jon Hunter <jonathanh@...dia.com>, 
	Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>, Prabhakar <prabhakar.csengg@...il.com>, 
	Catalin Marinas <catalin.marinas@....com>, Will Deacon <will@...nel.org>, 
	Bjorn Andersson <bjorn.andersson@....qualcomm.com>, linux-arm-kernel@...ts.infradead.org, 
	linux-kernel@...r.kernel.org, linux-renesas-soc@...r.kernel.org, 
	Biju Das <biju.das.jz@...renesas.com>, Fabrizio Castro <fabrizio.castro.jz@...esas.com>, 
	Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>, "linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>, 
	Arnd Bergmann <arnd@...db.de>
Subject: Re: [PATCH] arm64: defconfig: Build STMMAC Ethernet driver into the
 kernel for NFS boot

On Thu, Jun 12, 2025 at 02:34:32PM +0200, Geert Uytterhoeven wrote:
> Hi Jon,
> 
> CC Arnd
> 
> On Thu, 12 Jun 2025 at 14:20, Jon Hunter <jonathanh@...dia.com> wrote:
> > On 23/05/2025 12:54, Krzysztof Kozlowski wrote:
> > > On 23/05/2025 13:39, Geert Uytterhoeven wrote:
> > >> On Tue, 6 May 2025 at 12:47, Prabhakar <prabhakar.csengg@...il.com> wrote:
> > >>> From: Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>
> > >>>
> > >>> Enable `CONFIG_STMMAC_ETH` as built-in (`y`) instead of a module (`m`) to
> > >>> ensure the Ethernet driver is available early in the boot process. This
> > >>> is necessary for platforms mounting the root filesystem via NFS, as the
> > >>> driver must be available before the root filesystem is accessed.
> > >>>
> > >>> Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>
> > >>> ---
> > >>> With this change, the Renesas RZ/V2H EVK board can boot from NFS
> > >>> which has the DWMAC IP.
> > >>
> > >> Reviewed-by: Geert Uytterhoeven <geert+renesas@...der.be>
> > >> i.e. will queue in renesas-devel for v6.17.
> > >
> > > With my Nacked, please.
> >
> > I was surprised to see this change in -next. We also use NFS for testing
> > and we use the dwmac drivers. To date we are explictly building these
> > drivers into the initramfs but I noticed that that is now failing
> > because this driver is no longer a module by default. This is easy for
> 
> Oops, sorry for that...
> 
> > us to fix.
> 
> Good ;-)
> 
> > I do agree that if we start to build every networking driver into the
> > kernel it is going to bloat. Yes I do see the kernel image growing
> > regardless of this, but nonetheless it seems better to just build as a
> > module IMO.
> 
> Not _every_ networking driver, of course.  AFAIK, making network
> drivers built-in for systems where development is done using nfsroot
> has always been acceptable for the arm64 defconfig before.  For things
> not critical for booting, modular is indeed the preferred way.

Last time I tried to merge something like this I was told that we
shouldn't bloat the kernel for everyone just for our own convenience. I
tend to agree with this now. It's trivial to make local adjustments for
things like this. In fact, that's what I do all the time. I will use
defconfig as a base line and if I want the convenience of having network
drivers included because I don't want to update the initramfs every time
I update the kernel, I'll just change the driver to built-in in my local
.config.

I think of the defconfig as more of a reference for what a typical
development system would need. So it gives you reasonable build coverage
and such for a wide variety of boards.

If we start building too many things into the kernel, then at some point
it's going to become uselessly large for everyone. That's essentially
trading everyone's convenience for your own.

> BTW, we have other low-hanging fruit to fix, though:
> 
> CONFIG_SOUND=y
> CONFIG_SND=y
> CONFIG_SND_SOC=y
> CONFIG_SND_SOC_SAMSUNG=y (Krzysztof? ;-)
> CONFIG_USB=y

Yeah, there's probably a lot of options that could be changed to modules
to improve things. But perhaps we can start by not making things worse.

Thierry

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