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Date:   Tue, 4 Apr 2017 14:30:27 +0100
From:   Lee Jones <lee.jones@...aro.org>
To:     Hans Verkuil <hverkuil@...all.nl>
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 Tue, 04 Apr 2017, Hans Verkuil wrote:

> 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.

I have an idea.  Please bear with me.

-- 
Lee Jones
Linaro STMicroelectronics Landing Team Lead
Linaro.org │ Open source software for ARM SoCs
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