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

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Message-ID: <1d9285d3-54cd-0f9b-60c0-aed132aee72e@gmail.com>
Date:   Sun, 9 Jul 2017 00:42:58 -0700
From:   "Kuppuswamy, Sathyanarayanan" <sathyaosid@...il.com>
To:     Peter Rosin <peda@...ntia.se>,
        Andy Shevchenko <andy.shevchenko@...il.com>,
        Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 1/1] mux: consumer: Add dummy functions for
 !CONFIG_MULTIPLEXER case

Hi,


On 7/8/2017 11:59 PM, Peter Rosin wrote:
> 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?
I used ENODEV to signify that the MUX device is not available/enabled.
>
> And again, all these stubs should all be inlines, or things will break it
> this file is included more than once.
I will fix the inline problem in next version.
>
>>> 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.
Agreed. Since it returns the total number of MUX states, 0 seems to more
appropriate. I can fix it in next version.
>
>>> +}
>>> +
>>> +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
>>>
>>
>>