netdev - Re: [PATCH net-next v2 3/3] net: dsa: realtek: support reset controller

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Date: Thu, 2 Nov 2023 15:59:48 +0100
From: Linus Walleij <linus.walleij@...aro.org>
To: Luiz Angelo Daros de Luca <luizluca@...il.com>
Cc: Vladimir Oltean <olteanv@...il.com>, netdev@...r.kernel.org, alsi@...g-olufsen.dk, 
	andrew@...n.ch, vivien.didelot@...il.com, f.fainelli@...il.com, 
	davem@...emloft.net, kuba@...nel.org, pabeni@...hat.com, robh+dt@...nel.org, 
	krzk+dt@...nel.org, arinc.unal@...nc9.com
Subject: Re: [PATCH net-next v2 3/3] net: dsa: realtek: support reset controller

On Wed, Nov 1, 2023 at 8:55 PM Luiz Angelo Daros de Luca
<luizluca@...il.com> wrote:

> > drivers/net/dsa/realtek/Makefile
> > -obj-$(CONFIG_NET_DSA_REALTEK_MDIO)     += realtek-mdio.o
> > -obj-$(CONFIG_NET_DSA_REALTEK_SMI)      += realtek-smi.o
> > +obj-$(CONFIG_NET_DSA_REALTEK_MDIO)     += realtek-mdio.o realtek_common.o
> > +obj-$(CONFIG_NET_DSA_REALTEK_SMI)      += realtek-smi.o realtek_common.o
>
> Just a follow up.
>
> It is not that simple to include a .c file into an existing single
> file module. It looks like you need to rename the original file as all
> linked objects must not conflict with the module name. The kernel
> build seems to create a new object file for each module. Is there a
> clearer way? I think #include a common .c file would not be
> acceptable.

I don't know if this is an answer to your question, but look at what I did in

drivers/usb/fotg210/Makefile:

# This setup links the different object files into one single
# module so we don't have to EXPORT() a lot of internal symbols
# or create unnecessary submodules.
fotg210-objs-y                          += fotg210-core.o
fotg210-objs-$(CONFIG_USB_FOTG210_HCD)  += fotg210-hcd.o
fotg210-objs-$(CONFIG_USB_FOTG210_UDC)  += fotg210-udc.o
fotg210-objs                            := $(fotg210-objs-y)
obj-$(CONFIG_USB_FOTG210)               += fotg210.o

Everything starting with CONFIG_* is a Kconfig option obviously.

The final module is just one file named fotg210.ko no matter whether
HCD (host controller), UDC (device controller) or both parts were
compiled into it. Often you just need one of them, sometimes you may
need both.

It's a pretty clean example of how you do this "one module from
several optional parts" using Kbuild.

It's not super-intuitive, copy/paste/modify is a viable way to get to this.

Yours,
Linus Walleij