netdev - Re: [PATCH 08/17] can: add ISO 15765-2:2016 transport protocol

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Date:   Sat, 10 Oct 2020 18:24:48 +0200
From:   Oliver Hartkopp <socketcan@...tkopp.net>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     Marc Kleine-Budde <mkl@...gutronix.de>, netdev@...r.kernel.org,
        davem@...emloft.net, linux-can@...r.kernel.org,
        kernel@...gutronix.de
Subject: Re: [PATCH 08/17] can: add ISO 15765-2:2016 transport protocol



On 10.10.20 17:44, Jakub Kicinski wrote:
> On Sat, 10 Oct 2020 16:29:06 +0200 Oliver Hartkopp wrote:
>>>> diff --git a/net/can/Kconfig b/net/can/Kconfig
>>>> index 25436a715db3..021fe03a8ed6 100644
>>>> --- a/net/can/Kconfig
>>>> +++ b/net/can/Kconfig
>>>> @@ -55,6 +55,19 @@ config CAN_GW
>>>>    
>>>>    source "net/can/j1939/Kconfig"
>>>>    
>>>> +config CAN_ISOTP
>>>> +	tristate "ISO 15765-2:2016 CAN transport protocol"
>>>> +	default y
>>>
>>> default should not be y unless there is a very good reason.
>>> I don't see such reason here. This is new functionality, users
>>> can enable it if they need it.
>>
>> Yes. I agree. But there is a good reason for it.
>> The ISO 15765-2 protocol is used for vehicle diagnosis and is a *very*
>> common CAN bus use case.
> 
> More common than j1939? (Google uses words like 'widely used' and
> 'common' :)) To give you some perspective we don't enable Ethernet
> vlan support by default, vlans are pretty common, too.
> 
>> The config item only shows up when CONFIG_CAN is selected and then ISO
>> 15765-2 should be enabled too. I have implemented and maintained the
>> out-of-tree driver for ~12 years now and the people have real problems
>> using e.g. Ubuntu with signed kernel modules when they need this protocol.
>>
>> Therefore the option should default to 'y' to make sure the common
>> distros (that enable CONFIG_CAN) enable ISO-TP too.
> 
> I understand the motivation, but Linus had pushed back on defaulting to
> 'y' many times over the years, please read this:
> 
> https://lkml.org/lkml/2012/1/6/354
> 
> This really must not pop up on his screen as default 'y' when he does
> an oldconfig after pulling the networking tree..
> 

Ok. Understood.

I'll remove the default=y then. Would it be ok to add some text like

If you want to perfrom automotive vehicle diagnostic services (UDS), say 
'y'.

?

Best regards,
Oliver