netdev - Re: [PATCH] s390/net: lcs: fix build errors when FDDI is a loadable module

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Date: Thu, 22 Jun 2023 14:16:04 +0200
From: Alexandra Winter <wintera@...ux.ibm.com>
To: Simon Horman <simon.horman@...igine.com>
Cc: Randy Dunlap <rdunlap@...radead.org>, linux-kernel@...r.kernel.org,
        kernel test robot <lkp@...el.com>, Wenjia Zhang <wenjia@...ux.ibm.com>,
        linux-s390@...r.kernel.org, netdev@...r.kernel.org,
        Heiko Carstens <hca@...ux.ibm.com>, Vasily Gorbik <gor@...ux.ibm.com>,
        Alexander Gordeev <agordeev@...ux.ibm.com>,
        Christian Borntraeger <borntraeger@...ux.ibm.com>,
        Sven Schnelle <svens@...ux.ibm.com>,
        "David S . Miller"
 <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>
Subject: Re: [PATCH] s390/net: lcs: fix build errors when FDDI is a loadable
 module



On 22.06.23 09:53, Simon Horman wrote:
> On Thu, Jun 22, 2023 at 09:15:24AM +0200, Alexandra Winter wrote:
>>
>>
>> On 21.06.23 23:37, Randy Dunlap wrote:
>>> Require FDDI to be built-in if it is used. LCS needs FDDI to be
>>> built-in to build without errors.
>>>
>>> Prevents these build errors:
>>> s390-linux-ld: drivers/s390/net/lcs.o: in function `lcs_new_device':
>>> drivers/s390/net/lcs.c:2150: undefined reference to `fddi_type_trans'
>>> s390-linux-ld: drivers/s390/net/lcs.c:2151: undefined reference to `alloc_fddidev'
>>>
>>> This FDDI requirement effectively restores the previous condition
>>> before the blamed patch, when #ifdef CONFIG_FDDI was used, without
>>> testing for CONFIG_FDDI_MODULE.
>>>
>>> Fixes: 128272336120 ("s390/net: lcs: use IS_ENABLED() for kconfig detection")
[...]
> 
>> 2) I wonder whether
>>
>>   	depends on CCW && NETDEVICES && (ETHERNET || FDDI)
>>  +	depends on FDDI || FDDI=n
>>
>> would do what we want here:
>> When FDDI is a loadable module, LCS mustn't be built-in.
>>
>> I will do some experiments and let you know.
> 
> It does seem to on my side.
> But checking would be much appreciated.
 

Here are my experiments:

Current net-next:
-----------------
if !IS_ENABLED(CONFIG_ETHERNET) && !IS_ENABLED(CONFIG_FDDI)

drivers/s390/net/KConfig:
config LCS
	def_tristate m
	depends on CCW && NETDEVICES && (ETHERNET || FDDI)

.config:
ETHERNET  |  FDDI | LCS choices | LCS | compile
--------------------------------------------------------
n		m	m,n	  m	success (failed before Randy's fix)
y		m	y,m,n	  m	success (failed before Randy's fix)
y		m		  y	fails: undefined reference to `fddi_type_trans'


Simon's proposal:
-----------------
        depends on CCW && NETDEVICES && (ETHERNET || FDDI)
+       depends on FDDI=y || FDDI=n

ETHERNET  |  FDDI | LCS choices | LCS | compile
--------------------------------------------------------
n		m	-
y		m	-
y		m	-
y		n	y,m,n	  y	success
y		n	y,m,n	  m	success
y		y	y,m,n	  m	success


Alexandra's proposal:
---------------------
        depends on CCW && NETDEVICES && (ETHERNET || FDDI)
+       depends on FDDI || FDDI=n

ETHERNET  |  FDDI | LCS choices | LCS | compile
--------------------------------------------------------
n		m	m,n	  m	success
y		m	m,n	  m	success
y		n	y,m,n	  y	success
y		n	y,m,n	  m	success
y		y	y,m,n	  m	success

-----------------------------------------------------------

Seems that 
	A[tristate] depends on B[tristate]
means that A cannot be 'higher' than B.
Meaning, if B=n -> A= must be n
	if B=m -> A can be m or n
	if B=y -> A can be y or m or n

Although I did not find documentation confirming that.


@Randy, do you want give a v2 a try with that?

I guess then it is safe to delete from drivers/s390/net/lcs.c
-#if !IS_ENABLED(CONFIG_ETHERNET) && !IS_ENABLED(CONFIG_FDDI)
-#error Cannot compile lcs.c without some net devices switched on.
-#endif