linux-kernel - Re: [PATCH v2 1/1] mux: consumer: Add dummy functions for !CONFIG

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Date:   Sun, 9 Jul 2017 08:59:57 +0200
From:   Peter Rosin <peda@...ntia.se>
To:     Andy Shevchenko <andy.shevchenko@...il.com>,
        Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Sathyanarayanan Kuppuswamy Natarajan <sathyaosid@...il.com>
Subject: Re: [PATCH v2 1/1] mux: consumer: Add dummy functions for
 !CONFIG_MULTIPLEXER case

On 2017-07-08 23:22, Andy Shevchenko wrote:
> On Sat, Jul 8, 2017 at 9:12 PM,
> <sathyanarayanan.kuppuswamy@...ux.intel.com> wrote:
>> From: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com>
>>
>> Add dummy functions to avoid compile time issues when CONFIG_MULTIPLEXER
>> is not enabled.
>>
> 
> I don't think the error return code is okay to all of them. The return
> value should be choosen carefully (for some functions it's okay IMO to
> return 0).

BTW, is ENODEV correct for this situation? I have this nagging feeling
that ENODEV is over-used?

And again, all these stubs should all be inlines, or things will break it
this file is included more than once.

>> Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com>
>> ---
>>  include/linux/mux/consumer.h | 38 ++++++++++++++++++++++++++++++++++++++
>>  1 file changed, 38 insertions(+)
>>
>> Changes since v1:
>>  * Changed #ifdef to #if IS_ENABLED.
>>
>> diff --git a/include/linux/mux/consumer.h b/include/linux/mux/consumer.h
>> index 5577e1b..df78988 100644
>> --- a/include/linux/mux/consumer.h
>> +++ b/include/linux/mux/consumer.h
>> @@ -16,6 +16,7 @@
>>  struct device;
>>  struct mux_control;
>>
>> +#if IS_ENABLED(CONFIG_MULTIPLEXER)
>>  unsigned int mux_control_states(struct mux_control *mux);
>>  int __must_check mux_control_select(struct mux_control *mux,
>>                                     unsigned int state);
>> @@ -29,4 +30,41 @@ void mux_control_put(struct mux_control *mux);
>>  struct mux_control *devm_mux_control_get(struct device *dev,
>>                                          const char *mux_name);
>>
>> +#else
>> +unsigned int mux_control_states(struct mux_control *mux)
>> +{
>> +       return -ENODEV;
> 
> Peter, is here we are obliged to return error code in such case?

Since it will presumably be difficult to obtain a mux_control
w/o the mux-core being present, it doesn't matter much what
most of these stubs return.

For this stub, 0 is perhaps best, since the kernel-doc for
mux_control_states mentions nothing about any error possibility.

>> +}
>> +
>> +int __must_check mux_control_select(struct mux_control *mux,
>> +                                   unsigned int state)
>> +{
>> +       return -ENODEV;
> 
> return 0; ?

Maybe. But it doesn't matter much, but in this case the consumer must
handle errors. See above.

>> +}
>> +
>> +int __must_check mux_control_try_select(struct mux_control *mux,
>> +                                       unsigned int state)
>> +{
>> +       return -ENODEV;
>> +}
> 
> return 0; ?

Maybe. But it doesn't matter much, but in this case the consumer must
handle errors. See above.

>> +
>> +int mux_control_deselect(struct mux_control *mux)
>> +{
>> +       return -ENODEV;
>> +}
> 
> return 0; ?

Probably. See above.

Cheers,
peda

>> +
>> +struct mux_control *mux_control_get(struct device *dev, const char *mux_name)
>> +{
>> +       return ERR_PTR(-ENODEV);
>> +}
>> +
>> +void mux_control_put(struct mux_control *mux) {}
>> +
>> +struct mux_control *devm_mux_control_get(struct device *dev,
>> +                                        const char *mux_name)
>> +{
>> +       return ERR_PTR(-ENODEV);
>> +}
>> +#endif
>> +
>>  #endif /* _LINUX_MUX_CONSUMER_H */
>> --
>> 2.7.4
>>
> 
> 
>