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Date:   Tue, 4 Apr 2017 15:14:32 +0200
From:   Hans Verkuil <hverkuil@...all.nl>
To:     Lee Jones <lee.jones@...aro.org>
Cc:     hans.verkuil@...co.com, mchehab@...nel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        kernel@...inux.com, patrice.chotard@...com,
        linux-media@...r.kernel.org, benjamin.gaignard@...com
Subject: Re: [PATCH 1/2] [media] cec: Move capability check inside #if

On 04/04/2017 03:01 PM, Lee Jones wrote:
> On Tue, 04 Apr 2017, Lee Jones wrote:
> 
>> On Tue, 04 Apr 2017, Hans Verkuil wrote:
>>
>>> On 04/04/2017 02:32 PM, Lee Jones wrote:
>>>> If CONFIG_RC_CORE is not enabled then none of the RC code will be
>>>> executed anyway, so we're placing the capability check inside the
>>>>
>>>> Signed-off-by: Lee Jones <lee.jones@...aro.org>
>>>> ---
>>>>  drivers/media/cec/cec-core.c | 2 +-
>>>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>>>
>>>> diff --git a/drivers/media/cec/cec-core.c b/drivers/media/cec/cec-core.c
>>>> index 37217e2..06a312c 100644
>>>> --- a/drivers/media/cec/cec-core.c
>>>> +++ b/drivers/media/cec/cec-core.c
>>>> @@ -234,10 +234,10 @@ struct cec_adapter *cec_allocate_adapter(const struct cec_adap_ops *ops,
>>>>  		return ERR_PTR(res);
>>>>  	}
>>>>  
>>>> +#if IS_REACHABLE(CONFIG_RC_CORE)
>>>>  	if (!(caps & CEC_CAP_RC))
>>>>  		return adap;
>>>>  
>>>> -#if IS_REACHABLE(CONFIG_RC_CORE)
>>>>  	/* Prepare the RC input device */
>>>>  	adap->rc = rc_allocate_device(RC_DRIVER_SCANCODE);
>>>>  	if (!adap->rc) {
>>>>
>>>
>>> Not true, there is an #else further down.
>>
>> I saw the #else.  It's inert code that becomes function-less.
>>
>>> That said, this code is clearly a bit confusing.
>>>
>>> It would be better if at the beginning of the function we'd have this:
>>>
>>> #if !IS_REACHABLE(CONFIG_RC_CORE)
>>> 	caps &= ~CEC_CAP_RC;
>>> #endif
>>>
>>> and then drop the #else bit and (as you do in this patch) move the #if up.
>>>
>>> Can you make a new patch for this?
>>
>> Sure.
> 
> No wait, sorry!  This patch is the correct fix.
> 
> 'caps' is already indicating !CEC_CAP_RC, which is right.
> 
> What we're trying to do here is only consider looking at the
> capabilities if the RC Core is enabled.  If it is not enabled, the #if
> still does the right thing and makes sure that the caps are updated.
> 
> Please take another look at the semantics.

Ah, yes. You are right. But so am I: the code is just unnecessarily confusing
as is seen by this discussion.

I still would like to see a patch with my proposed solution. The control flow
is much easier to understand that way.

Regards,

	Hans

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