linux-kernel - Re: drivers/net/dsa/dsa_loop

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Date: Thu, 16 May 2024 11:17:15 +0900
From: Masahiro Yamada <masahiroy@...nel.org>
To: Florian Fainelli <f.fainelli@...il.com>
Cc: Andrew Lunn <andrew@...n.ch>, Stephen Langstaff <stephenlangstaff1@...il.com>, 
	Alexander Lobakin <aleksander.lobakin@...el.com>, 
	Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>, linux-kernel@...r.kernel.org, 
	OlteanV@...il.com
Subject: Re: drivers/net/dsa/dsa_loop_bdinfo.c build problems

On Thu, May 16, 2024 at 4:21 AM Florian Fainelli <f.fainelli@...il.com> wrote:
>
> Adding Olek and Masahiro,
>
> On 5/14/24 21:05, Florian Fainelli wrote:
> >
> >
> > On 5/14/2024 9:17 AM, Andrew Lunn wrote:
> >> On Tue, May 14, 2024 at 05:08:24PM +0100, Stephen Langstaff wrote:
> >>> On Tue, May 14, 2024 at 1:32 PM Andrew Lunn <andrew@...n.ch> wrote:
> >>>
> >>>> So try to making FIXED_PHY = m, and load it after dsa_loop_bdinfo.ko.
> >>>
> >>> In my configuration FIXED_PHY is selected by several other modules:
> >>>    │ Selected by [y]:
> >>>    │   - FSL_DPAA_ETH [=y] && NETDEVICES [=y] && ETHERNET [=y] &&
> >>> NET_VENDOR_FREESCALE [=y] && FSL_DPAA [=y] && FSL_FMAN [=y]
> >>>    │   - FWNODE_MDIO [=y] && NETDEVICES [=y] && MDIO_DEVICE [=y] &&
> >>> (ACPI [=y] || OF [=y] || COMPILE_TEST [=n])
> >>>    │   - OF_MDIO [=y] && NETDEVICES [=y] && MDIO_DEVICE [=y] && OF [=y]
> >>> && PHYLIB [=y]
> >>>
> >>> ...so it looks pretty tied up with the MDIO support which I guess I
> >>> will need for the real PHY!
> >>>
> >>> If I sorted out building the dsa_loop_bdinfo.c code as a built-in do
> >>> you think that would solve the ordering issue?
> >
> > I have re-created the issue with CONFIG_FIXED_PHY=y and for a reason I
> > do not yet understand the following rule:
> >
> > obj-$(CONFIG_FIXED_PHY)                += dsa_loop_bdinfo.o
> >
> > does not result in the kernel image containing the dsa_loop_bdinfo.o
> > object symbols. I am fairly sure this worked when this was submitted
> > back then, so give me a day or two to figure out why. AFAICT the make
> > rule is simply not executed.
>
> Bisection landed on 227d72063fccb2d19b30fb4197fba478514f7d83 ("dsa:
> simplify Kconfig symbols and dependencies") which appeared in v5.13 and
> specifically this hunk being reverted back to how it was before gets us
> the build results we want:
>
> diff --git a/drivers/net/Makefile b/drivers/net/Makefile
> index 7ffd2d03efaf..5da6424bc6f8 100644
> --- a/drivers/net/Makefile
> +++ b/drivers/net/Makefile
> @@ -45,7 +45,7 @@ obj-$(CONFIG_ARCNET) += arcnet/
>   obj-$(CONFIG_DEV_APPLETALK) += appletalk/
>   obj-$(CONFIG_CAIF) += caif/
>   obj-$(CONFIG_CAN) += can/
> -obj-$(CONFIG_NET_DSA) += dsa/
> +obj-y += dsa/
>   obj-$(CONFIG_ETHERNET) += ethernet/
>   obj-$(CONFIG_FDDI) += fddi/
>   obj-$(CONFIG_HIPPI) += hippi/
>
> Masahiro, for context in drivers/net/dsa/Makefile we have this bit:
>
> obj-$(CONFIG_NET_DSA_LOOP)      += dsa_loop.o
> ifdef CONFIG_NET_DSA_LOOP
> obj-$(CONFIG_FIXED_PHY)         += dsa_loop_bdinfo.o
> endif
>
> whereby we want dsa_loop.o to follow the value of CONFIG_NET_DSA_LOOP,
> and we want dsa_loop_bdinfo.o to be either built as a module or built
> into the kernel and we want to follow the value of CONFIG_FIXED_PHY
> because there is a functional dependency between the two objects.
>
> Prior to Olek's change this would work just fine because we would always
> descend into drivers/net/dsa/ but after his change, and assuming that
> CONFIG_NET_DSA=m which is the case, then we no longer get
> dsa_loop_bdinfo.o to be built at all when CONFIG_FIXED_PHY=y.
> Essentially only obj-m rules are being processed, obj-y rules are not.
>
> That does not really seem intuitive to me as to why any suggestions on
> how to fix that, short of unconditionally descending into the tree like
> we used to?



"obj-m += dsa/" means everything under dsa/ must be modular.



If there is a built-in object under dsa/ with CONFIG_NET_DSA=m,
you cannot do  "obj-$(CONFIG_NET_DSA) += dsa/".


You need to change it back to "obj-y += dsa/".


>
> Reproducer configuration available here:
>
> https://gist.github.com/ffainelli/2650a832803b502b94b2d247209f61b1
>
> rm drivers/net/dsa/*.o
> ARCH=x86 make drivers/net/dsa/
> ls drivers/net/dsa/dsa_loop_bdinfo.o
>
> Thanks!
> --
> Florian
>


-- 
Best Regards
Masahiro Yamada