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

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Message-ID: <8a699761-de25-409d-9d8a-aa0c1ac4c605@gmail.com>
Date: Wed, 15 May 2024 20:35:06 -0700
From: Florian Fainelli <f.fainelli@...il.com>
To: Masahiro Yamada <masahiroy@...nel.org>
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 5/15/2024 7:17 PM, Masahiro Yamada wrote:
> 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/".

Thanks, posted a patch doing that! Is there anyway that Kbuild could be 
warning about such a situation?
-- 
Florian